Journal of Alloys and Compounds (v.478, #1-2)

In this study, CuInSe2 thin films were prepared by pulse-reverse electrodeposition and selenization process and characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). The pulse-deposited films show well adherent to the substrate and smooth surface with fine grains. The chalcopyrite structure of CuInSe2 with enhancement in crystallinity was observed for the films after selenization treatment in Se vapor. The best solar cell fabricated using the resultant films as absorber layers within a Ni–Al/ZnO:Al/i-ZnO//CdS/CIS/Mo/soda-lime glass structure showed an efficiency of 1.42% under AM 1.5 illumination.
Keywords: CuInSe2; Thin films; Pulse-reverse electrodeposition; Photovoltaics;

Dual amorphous phases with fractal morphology are observed in the ternary metallic Y–Ti–Co/Y–Nb–Co systems upon ion irradiation. Interestingly, the obtained dual amorphous phases in the two systems feature different fractal dimension. For Y–Ti–Co system, the fractal dimension is around 2.16 suggesting that it grows through Reaction-Limited-Cluster-Aggregation model. For Y–Nb–Co system, however, the fractal dimension is around 2.54, suggesting that it grows through Diffusion-Limited-Aggregation model.
Keywords: Metallic glasses; Dual phase; Fractal; Ion implantation;

We report on the formation and electrochemical properties of Co3O4/Pt nanocomposite electrodes, which were fabricated by an RF magnetron co-sputtering system, for micro-electrochemical capacitors. High-resolution electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy examinations are performed to characterize the structural and chemical properties of the Co3O4/Pt nanocomposite electrodes. It is shown that the Co3O4/Pt6020 nanocomposite electrodes where RF powers of 60 and 20 W were applied to Co3O4 and Pt targets, respectively, give capacitance of 391.6 F/cm3 at 100 mV/s along with superb high-rate performance, which is much higher that those of Co3O4 only and other nanocomposite electrodes. The improvement is explained in terms of the formation of Co3O4–Pt combined nanostructures and their good electrical conductivity.
Keywords: Electrode materials; Nanostructured materials; Eelectrochemical reactions;

Study on adsorption of N2 and O2 by magnesium (II)-exchanged zeolite A by Yunshuai Shang; Jian Wu; Jiang Zhu; Yu Wang; Changgong Meng (L5-L7).
The magnesium (II)-exchanged zeolite A (MgA) was prepared by cation exchange process using sodium form zeolite A (NaA) and MgCl2 in aqueous solution. The prepared MgA was characterized by infrared spectroscopy and X-ray powder diffraction analysis. The results showed that the LTA structure remains after cation exchange. A static volumetric system was employed to evaluate the N2 and O2 adsorption properties of all the samples at 298 K. It was found that the N2 adsorption capacity of MgA increased rapidly with pressure rise, and the adsorption isotherm of N2 became nonlinear in low pressure region. The O2 adsorption capacity of MgA increased slightly with pressure. The introducing Mg2+ into the sodium type zeolite A greatly enhanced the N2 adsorption capacity. The highest N2 adsorption capacity and N2/O2 selectivity appeared in the sample with 64.3% of Mg2+ replaced.
Keywords: Inorganic materials; Chemical synthesis; Liquid–solid reactions; X-ray diffraction;

By introducing the inert salt CaF2 as dispersant, a convenient low-temperature CVD method has been developed to grow low-melting-point-metal nitride or oxide nanostructures, such as GaN nanowires, AlN nanorods, Ga2O3 nanowires and nanobelts, SnO2 nanorods and nanobelts, In2O3 nanosheets and nanowires. All the materials above were successfully grown on Si substrates through the direct nitridation or oxidation of metals–CaF2 mixture in the range of 650–750 °C. Compared with the necessary temperatures previously reported also through the direct nitridation or oxidation of low-melting-point-metal powders, herein low-temperature synthesis could be attributed to the dispersion of inert salt CaF2 which help to substantially increase the surface areas and the vapor pressures of the corresponding metal precursors. The simplicity of the preparation procedure and the wide potential applications of this route make this study technologically interesting.
Keywords: Semiconductors; Nanostructured materials; Nitride materials; Oxide materials; Vapor deposition;

A new structural type has been found for the compound with nominal composition (Mg x Ca1−x )Ni2.6. Its structure is made of nine layers (6 AB2  + 3 AB5) stacked in an original manner. The average structure may be regarded as a Gd2Co7 type-structure in which half of the AB5 blocks have been replaced by AB2 blocks. The hydrogen sorption properties are similar to those of the Ca0.4Mg0.6Ni3 compound with the PuNi3 structure. However, the resulting arrangement departs significantly from the PuNi3 structural type since a symmetry reduction from R-3m into R3 takes place.
Keywords: Hydrogen absorbing materials; Crystal structure;

β-Nickel hydroxide crystallizes in brucite structure with a stacking of charge neutral Ni(OH)2 layers represented by AbC. A and C represent the hydroxide ions while b denotes the nickel ion. Crystalline nickel hydroxide having ideal composition will have the stacking sequence of AbC AbC AbC … . When the stacking sequence of nickel hydroxide is different from that of the ideal i.e. AbC AbC BcA …, then the sample is stacking faulted. Highly disordered βbc-nickel hydroxide comprises of an intergrowth of α-phase of nickel hydroxide in β-nickel hydroxide. These disorders introduce a significant changes in their structure composition and morphological features in contrast to crystalline phase of β-nickel hydroxide. The tap densities of all these nickel hydroxide samples were investigated. Electrochemical performance of crystalline phase β-nickel hydroxide with high tap density exchanges 0.3 e/Ni while nickel hydroxide samples with stacking disorder or compositional disorder exchanges 0.8–0.9 e/Ni. These samples have lower tap densities compared to crystalline β-nickel hydroxide. The results clearly show that the better electrochemical activity is mainly dictated by the structural disorder and is not associated to tap density of nickel hydroxide.
Keywords: Electrochemical activity; Nickel hydroxide; Structural disorder; Tap density;

Fabrication, microstructure and optical properties of titanium doped YAG transparent ceramic by Tongde Huang; Benxue Jiang; Yusong Wu; Jiang Li; Yun Shi; Wenbin Liu; Yubai Pan; Jingkun Guo (L16-L20).
Highly transparent titanium doped Y3Al5O12 (YAG) ceramic for the first time was fabricated by solid-state reaction method, which was sintered at 1770 °C for 10 h under the vacuum condition. The transmittance of the sample reached as high as 80% in the infrared region. The microstructure and the optical properties of the ceramics varied obviously with three different annealing conditions: in air, under vacuum, and in both air and then under vacuum, and these three kinds of ceramics were named as: Sample A, Sample B, and Sample C in sequence. There existed numerous impurity phases in both Sample B and Sample C, which were experimentally speculated as Al2O3 and Y2Ti2O7. Only the Sample A kept no any other phase or pore and displayed uniform grains. Furthermore, three absorption peaks of Sample A at about 400, 498 and 586 nm all coexisted with the Ti3+ ion and disappeared as soon as the ceramic was treated in air. The X-ray fluorescence of Sample B showed a peak at about 500 nm, but Sample A showed no peak. The intense photoluminescence peaks at about 775 and 810 nm of the ceramic excited by 532 nm laser diode system may demonstrate that Ti:YAG ceramic could be a promising laser material.
Keywords: Optical materials; Sintering; Microstructure; Optical properties;

Keywords (I-II).

The reactions between Cu and the Sn2.5Ag0.8Cu solders doped with 0, 0.005, 0.01, 0.03, 0.06, or 0.1 wt.% Ni were studied. Reaction conditions included multiple reflows and solid-state aging at 160 °C. The Ni additions produced much thinner Cu3Sn layers for all the Ni concentrations used. Ni concentration higher than 0.01 wt.% could effectively retard the Cu3Sn growth even after 2000 h of aging, and accordingly 0.01 wt.% can be considered the minimum effective Ni addition.
Keywords: Soldering; Diffusion; Intermetallics;

Magnetism in REPdSn (RE  = La, Pr, Nd) compounds: A single-crystal study by M. Mihalik; M. Diviš; H. Kitazawa; V. Sechovský (1-8).
The lack of data obtained on single crystals of the REPdSn intermetallic compounds (RE  = La, Pr, Nd) motivated us to grow single crystals of these compounds and to study intrinsic magnetic and related electronic and thermal properties of these materials with an emphasis on magnetocrystalline anisotropy. All the three compounds crystallize in the orthorhombic TiNiSi-type crystal structure. The results of specific heat, magnetization and resistivity measurements have revealed that LaPdSn is a paramagnet at temperatures down to 2 K, PrPdSn and NdPdSn order antiferromagnetically below T N  = 4.2(1) and 3.4(1) K, respectively, and exhibit considerable magnetocrystalline anisotropy. The latter compound undergoes an order-to-order phase transition at 1.9(3) K. At sufficiently high temperatures the susceptibility of the Pr- and Nd-compounds follows a Curie–Weiss law with the effective magnetic moment almost identical in all the three principal crystallographic directions to the value expected for the corresponding free RE 3+ ion. The values of the paramagnetic Curie temperature manifest the anisotropy of the susceptibility in paramagnetic state, which is particularly pronounced for PrPdSn. As temperature decreases the susceptibility exhibits anisotropic departure from the Curie–Weiss behavior as a consequence of the crystal field (CF) influence on the RE ions. The involvement of the crystal field in the magnetism of the RE ions is also reflected in the Schottky contribution to the specific heat which reflects the splitting of the CF energy levels and the reduced values of the RE ordered magnetic moments due to the unpopulated higher-energy CF energy levels at low temperatures. Interesting features of magnetism in PrPdSn and NdPdSn are reflected also in the electrical resistivity and magnetoresistivity.For closer understanding of magnetism in the studied REPdSn compounds we have also performed first principles electronic structure calculations. We present the calculated density of states (DOS) of REPdSn compounds and we also compare the obtained experimental results with the theoretical predictions from the calculated electronic structure.
Keywords: Rare earth alloys and compounds; Crystal growth; Heat capacity; Phase transitions; Magnetic measurements;

La2Bi7Fe5Ti3O27: Structural, electrical and magnetic properties by S.K. Patri; R.N.P. Choudhary; M. Manivel Raja (9-13).
Ferroelectromagnetic, La2Bi7Fe5Ti3O27 compound was synthesized using a solid-state reaction technique. Basic crystal data of the compound were obtained by XRD. Detailed studies of electrical properties (i.e., dielectric and impedance) of the material carried out in wide frequency (102 to 106  Hz) and temperatures (30 to 500 °C) ranges showed that these properties are strongly dependent on frequency and temperature. Magnetic measurements of the material provided a remanent magnetization of 0.011 emu/g at room temperature.
Keywords: Ceramics; Ferroelectrics; Sintering; Microstructure;

Antimony valence and the magnetization processes in the spinels (Cu)[CrSb]Se4 by J. Krok-Kowalski; J. Warczewski; P. Gusin; T. Śliwińska; G. Urban; E. Malicka; A. Pacyna; T. Mydlarz; P. Rduch; G. Władarz (14-18).
The spinel stoichiometric compounds of the CuCr2 −  x Sb x Se4 family were obtained for the first time and prepared with the assumption of the valence of Sb ions equal to 3. The magnetization isotherms at 4.2 K and at the magnetic stationary fields up to 14 T as well as the temperature dependencies of magnetic susceptibility were studied in the temperature range of 4.2 ÷ 400 K. These results were compared with analogous measurements performed earlier by the authors for the nonstoichiometric spinel family built of the same elements and obtained under the assumption of the valence of Sb ions equal to 5. From this comparison it follows that these two spinel series reveal significant differences: (1) The interval of possible concentrations of Sb ions in the obtained stoichiometric spinel samples under study is up to 1.0, whereas for the nonstoichiometric spinels is (0.30 ÷ 0.48). (2) The corresponding intervals for the appearance of the spin glass states are: (0.2 ÷ 1.0) and (0.30 ÷ 0.48), whereas the freezing temperatures do not differ significantly. (3) The magnetization processes in the stoichiometric samples depend strongly on the Sb concentration, whereas in the nonstoichiometric samples they run very hardly.
Keywords: Magnetically ordered materials; Semiconductors; Spin glasses; Magnetic measurements; Exchange and superexchange;

Specific heat measurements on amorphous and nanocrystalline Al88Y5Ni5Co2 by J.S. Blázquez; M. Millán; C.F. Conde; A. Conde; J. Latuch; T. Kulik (19-21).
Specific heat at constant pressure, C P , was measured on amorphous and nanocrystalline Al88Y5Ni5Co2 alloys from differential scanning calorimetry experiments. Linear behavior of C P versus temperature from 323 to 423 K is explained by conduction electrons contribution and dilatation correction factor. Results indicate that the Fermi energy increases as nanocrystallization progresses, although the estimated values are clearly lower than those found for crystalline Al.
Keywords: Specific heat; Nanocrystalline alloys;

Magnetic properties of Th3P4-type Tb4Sb3−X {Si, Ge, Bi} X solid solutions by A.V. Morozkin; D. Buddhikot; A.K. Nigam; O. Isnard; Y. Mozharivskyj (22-29).
The magnetic properties of Tb4Sb2Bi, Tb4Sb2.75Ge0.25 and Tb4Sb2.3Si0.7 solid solutions (Th3P4-type, cubic; cI28, space group I 4 ¯ 3 d , No. 220) have been investigated by means of magnetization and neutron diffraction studies. The magnetization measurements indicate that the Tb4Sb2Bi compound orders magnetically at 120 K (T N) and 50 K (T C). The magnetization vs. field isotherm at 5 K shows signature of ferromagnetic order. Neutron diffraction experiment in zero applied magnetic field shows that below T N  = 125(4) K Tb4Sb2Bi exhibits a antiferromagnetic flat spiral type ordering with wave vector K 1  = [±K X , ± K X , ± K X ] (K X value changes from 0.1033 up to 0.158 in the temperature interval down to 2 K). Below T m  = 70(4) K the decreasing of antiferromagnetic component coincides with increasing of the ferromagnetic component and about T CN  = 55(4) K, Tb4Sb2Bi shows ferromagnetic transition. At 2 K, the magnetic structure of Tb4Sb2Bi is ferromagnetic cone and the cone axis is along [1 1 1] direction.Neutron diffraction study of Tb4Sb2.75Ge0.25 indicate an antiferromagnetic ordering at 155(4) K (ferromagnetic cone with K 1  = [±0.136(2), ±0.136(2), ±0.136(2)]) and ferromagnetic ordering (sharp increasing of ferromagnetic component) at 145(4) K. The K X value is nearly constant from 155 K down to 2 K. At 2 K, the magnetic structure of Tb4Sb2.75Ge0.25 is ferromagnetic cone with a weak antiferromagnetic component and the cone axis is along [1 1 1] direction.Low field magnetisation measurements on Tb4Sb2.3Si0.7 indicate a ferromagnetic ordering at T C  ∼ 180 K. Thus small substitutions of Bi, Ge and Si at Sb-site of Tb4Sb3 are found to increase the magnetic ordering temperature of the parent compound.
Keywords: Rare earth intermetallics; Terbium bismuth antimonide; Terbium germanium antimonide; Terbium silicon antimonide; Magnetisation; Neutron diffraction; Magnetic structure;

Vibrational investigations of lanthanide doped strontium barium niobate (SBN) crystals by D. Kasprowicz; A. Lapinski; T. Runka; A. Speghini; M. Bettinelli (30-33).
Strontium barium niobate (Sr0.5Ba0.5Nb2O6 and Sr0.6Ba0.4Nb2O6) single crystals doped with 1–2.5 mol% of the luminescent ions Eu3+ and Er3+ have been investigated using Raman and IR spectroscopy. The vibrational spectra of SBN crystals are dominated by broad and multi-component bands related to the internal vibrations of the NbO6 7− octahedra. In order to interpret the experimental vibrational spectra of SBN crystals the quantum-chemical calculations (DFT) for the NbO6 7− anion have been carried out. As a first approximation, the dynamics of isolated NbO6 7− anions have been taken into account. The calculated vibrational frequencies for the free NbO6 7− ion are in fair agreement with the frequencies of modes observed in experiment. The discrepancies are attributed to the distortion of the niobate octahedra in the actual crystal structure and to the presence of disorder and doping with impurity ions in SBN crystals.
Keywords: Strontium barium niobate; Single crystals; Nanocrystals; Vibrational properties; DFT calculations;

Instability of the Co magnetic state in Y2Co7-based compounds: Effect of alloying for Y- and Co-sites by M.I. Bartashevich; N.V. Mushnikov; A.V. Andreev; T. Goto (34-37).
High field magnetization process has been studied in the (Y1−x Zr x )2Co7, (Y1−x U x )2Co7 and Y2(Co1−x Al x )7 systems in order to reveal the possibility of the transformation of the Co magnetic ions from the high to the low moment state. The spontaneous magnetic moment, Curie temperature and anisotropy constant have been found to decrease monotonously with increasing x in the single phase interval. The results suggest that the Co moment in present systems is unstable with respect to both electron concentration and exchange interactions. The average Co moment reduces to the value characteristic of the YCo3 compound. However, no signatures of the formation of the low moment Co state was found in the studied Y2Co7-based systems.
Keywords: Rare earth – 3d transition metal intermetallics; Magnetic properties; Itinerant electron metamagnetism; High field; Magnetocrystalline anisotropy;

Synthesis of iron oxide nanoneedles and their field emission properties by Xiaohuan Sun; Wentao Liu; Dongxun Ouyang (38-40).
In this paper, the fabrication of iron oxide (α-Fe2O3) nanoneedle arrays has been achieved. By thermally oxidizing iron plates at 650 °C under vacuum, nanoneedles with 2–5 μm in length are obtained with high yield. The diameters of the nanoneedle tips are typically as small as several nanometers. The field emission measurement shows that these nanoneedles have strong electron field emission abilities, with relatively low turn-on fields of 4.8 Vμm−1. This makes the Fe2O3 nanoneedle arrays one of the promising candidates as the field emitters.
Keywords: Nanostructured materials; Oxide materials; Electronic properties; X-ray diffraction;

Plasmon–phonon interaction in Hg1−x Mn x Se alloys by N. Romčević; M. Romčević; A. Milutinović; S. Kostić (41-44).
Far-infrared reflection and Raman spectra of Hg1−x Mn x Se (x  ≤ 0.3) alloys were measured at room temperature. The analysis of the Raman spectra was made by deconvolution technique. The analysis of the far-infrared spectra was made by a fitting procedure based on dielectric function which includes spacious distribution of free carrier influence on the plasmon–phonon interaction. In spite of strong plasmon–LO phonon interaction, we found that the long wavelength optical phonon modes of these mixed crystals showed two-mode behaviour. The model of phonon behaviour was developed, and we obtain very good agreement with experimental results.
Keywords: Semiconductors; Infrared spectroscopy; Optical properties; Light absorption and reflection;

Investigations of the properties of Zn1−x Cr x O thin films grown by RF magnetron sputtering by J. Elanchezhiyan; K.P. Bhuvana; N. Gopalakrishnan; B.C. Shin; W.J. Lee; T. Balasubramanian (45-48).
This work investigated the properties of Cr doped ZnO (Zn1−x Cr x O) thin films with different doping concentrations (x  = 0.05, 0.15, 0.30) on a Si (1 0 0) substrate using RF magnetron sputtering. These films have been characterized by powder X-ray diffraction (XRD), atomic force microscopy (AFM) and vibrating sample magnetometer (VSM) measurements to investigate structural, morphological and magnetic properties. XRD results reveal that the wurtzite structure deviates for the films with higher concentrations of Cr. The VSM measurements show the ferromagnetic behaviour for all the Cr doped ZnO films at room temperature.
Keywords: Thin films; Depositions; Magnetic materials; Atomic force microscopy;

Structural, dielectric and electrical properties of LiBaFeWO6 by M.P.K. Sahoo; N. Kumar; R.N.P. Choudhary (49-53).
The polycrystalline sample of LiBaFeWO6 was prepared by a high-temperature solid-state reaction technique. Preliminary structural analysis shows the formation of a new compound with an orthorhombic crystal structure at room temperature. The SEM micrograph shows the polycrystalline nature of the sample with different grain-size and inhomogeneous distribution. The temperature dependent dielectric and impedance behavior of the material was studied in a wide frequency (1 kHz–1 MHz) and temperature (30–480 °C) range. The nature of electrical conduction and relaxation is supported by hopping mechanism of ions and oxygen vacancies.
Keywords: Semiconductor; Grain boundaries; Scanning electron microscopy; X-ray diffraction; Dielectric response; Ionic conduction and relaxation;

Realization of p-type conduction in (ZnO)1−x (AlN) x thin films grown by RF magnetron sputtering by K.P. Bhuvana; J. Elanchezhiyan; N. Gopalakrishnan; B.C. Shin; T. Balasubramanian (54-58).
A different approach for codoping in ZnO using AlN as dopant (codopant) has been attempted to realize p-ZnO by RF magnetron sputtering. The (ZnO)1−x (AlN) x [AlN codoped ZnO] films of different doping concentrations (0.5, 1, 2 and 4 mol%) grown on Si(1 0 0) substrates have been subjected to X-ray diffraction (XRD) and Hall measurements to investigate their structural and electrical properties, respectively. XRD results reveal that all the films are constituted in wurtzite structure with the preferential orientation of (0 0 2) diffraction plane. It has been observed that the c-axis lattice constant is higher than unstressed bulk value for 0.5 and 1 mol% AlN doped ZnO films which support the incorporation of N atoms into the film. The Hall measurements show that the (ZnO)1−x (AlN) x films with 0.5 and 1 mol% of AlN exhibit p-type conduction with the carrier concentration of 9.797 × 1018/cm3 and 2.415 × 1019/cm3, respectively. The grain size observed through XRD is comparable to that observed through FESEM. The incorporation of nitrogen into the film upon doping of AlN is confirmed by Fourier transformed infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS).
Keywords: p-Type ZnO; RF magnetron sputtering; Codoping;

Microstructure, magnetic properties and magnetocaloric effect in melt-spun Ni–Mn–Ga ribbons by N.V. Rama Rao; R. Gopalan; V. Chandrasekaran; K.G. Suresh (59-62).
Structural transformation, microstructure and magnetocaloric effect (MCE) were investigated in melt-spun Ni55Mn20.6Ga24.4 and Ni55Mn19.6Ga25.4 ribbons. Magnetic and thermal studies of the ribbons revealed the occurrence of simultaneous structural and magnetic transitions near room temperature with a narrow thermal hysteresis of magnetization ≈2 K. Maximum entropy changes (ΔS M) of −9.5 and −10.4 J/kg K have been obtained at 309 K for a field change of 2 T in Ni55Mn20.6Ga24.4 and Ni55Mn19.6Ga25.4 ribbons, respectively. The Ni55Mn19.6Ga25.4 ribbon exhibits refrigeration capacity (RC) of 47 J/kg with low average hysteresis loss (≈1.5 J/kg) at the merged structural and magnetic transition temperature.
Keywords: Magnetocaloric; Rapid solidification; Magnetic measurements;

Spectroscopic studies of Eu3+ ions in LBTAF glasses by B.C. Jamalaiah; J. Suresh Kumar; A. Mohan Babu; L. Rama Moorthy (63-67).
Optical absorption, excitation and radiative properties of Eu3+ ions in lead borate titanate aluminium fluoride (LBTAF) glasses are reported. The observed energy levels are fitted to the free-ion Hamiltonian model (H FI ) by diagonalising the energy matrices of 4f6 electronic configuration. The effect of thermalization on the oscillator strengths of the absorption bands originating from the ground (7F0) and the first excited (7F1) states of Eu3+ ion is discussed. The phenomenological Judd–Ofelt (JO) parameters obtained by applying the thermal correction to 7F0  →  5D2 and 7F6 absorption oscillator strengths were used to calculate the spontaneous emission probabilities (A R ), radiative branching ratios (β R ) and lifetimes (τ R ) for the 5D0  →  7F J (J  = 0–6) emission levels. Room temperature luminescence spectra are recorded for different Eu3+ ion concentrations upon excitation at 393 nm, corresponding to 7F0  →  5L6 transition. The decay profiles of 5D0  →  7F2 transition in the present glasses are single exponential for all the concentrations. The experimental lifetimes (τ m ) are found to decrease with increase of Eu3+ ion concentration. The results of radiative properties confirm that LBTAF glasses doped with Eu3+ ions emit an intense red luminescence at 615 nm corresponding to 5D0  →  7F2 emission level.
Keywords: Glass; Optical Spectroscopy; Absorption; JO parameters; Luminescence; Europium ion;

Hydrogen in nonstoichiometric cubic niobium carbides: Neutron vibrational spectroscopy and neutron diffraction studies by A.V. Skripov; H. Wu; T.J. Udovic; Q. Huang; R. Hempelmann; A.V. Soloninin; A.A. Rempel; A.I. Gusev (68-74).
The vibrational spectra and positions of H(D) atoms in NbC1−y H x (D x ) (0.19 ≤  y  ≤ 0.29, 0.04 ≤  x  ≤ 0.30) have been studied by inelastic neutron scattering (INS) and neutron diffraction. The analysis of the neutron diffraction data for NbC0.76H x (D x ) and NbC0.71H x (D x ) has revealed a number of different structures depending on the carbon concentration and the presence of absorbed H(D) atoms: the partially ordered cubic P m 3 ¯ m structure for NbC0.76, the partially ordered orthorhombic Pmmm structure for NbC0.76D0.17 and NbC0.76H0.18, the disordered cubic F m 3 ¯ m structure for NbC0.71 and NbC0.71D0.30, and the disordered tetragonal I4/mmm structure for NbC0.71H0.28. The INS spectra of NbC0.81H x and NbC0.76H x (D x ) in the energy transfer range 40–140 meV are found to consist of a single fundamental peak due to hydrogen optical vibrations (centered at 98 meV for H and at 65 meV for D) and a single peak due to carbon optical vibrations (centered at 78 meV). In addition to these peaks, the INS spectrum of NbC0.71H0.28 exhibits a peak at 130 meV, suggesting that H atoms in this compound occupy the sites displaced from the centers of carbon vacancies.
Keywords: Hydrogen absorbing materials; Crystal structure; Inelastic neutron scattering; Neutron diffraction;

Precipitation of Ag2Te in the thermoelectric material AgSbTe2 by Joshua D. Sugar; Douglas L. Medlin (75-82).
The microstructure of AgSbTe2, prepared by solidification, is investigated using electron microscopy. During solidification and thermal treatment, the material separates into a two-phase mixture of a rocksalt phase, which is Ag22Sb28Te50, and silver telluride, Ag2Te. Ag2Te formation results either from eutectic solidification (large lamellar structures), or by solid-state precipitation (fine-scale particles). The crystal structure of the AgSbTe2 phase determined by electron diffraction is consistent with a rocksalt structure that has a disordered cation sublattice. A preferred crystallographic orientation relationship at the interface between the matrix and the low-temperature monoclinic Ag2Te phase is defined and discussed. This orientation relationship is observed for both second-phase morphologies. In both cases, the orientation relationship originates from a topotactic (cube-on-cube) alignment of the Te sublattices in the initially cubic Ag2Te and the matrix at elevated temperature. This Te sublattice alignment is retained as the Ag2Te undergoes a cubic-to-monoclinic transformation during cooling. This orientation relationship is observed for both second-phase morphologies.
Keywords: Thermoelectric materials; Precipitation; Phase transitions; TEM;

Electrocrystallization of Pb and Pb assisted Al on aluminum electrode from molten salt (AlCl3–NaCl–KCl) by M. Jafarian; I. Danaee; A. Maleki; F. Gobal; M.G. Mahjani (83-88).
Electrochemical deposition of aluminum and lead from basic molten AlCl3–NaCl–KCl mixture on an aluminum electrode at 180 °C was studied by the methods of voltammetry, potential and current transient and constant current deposition. The deposition of aluminum was found to proceed via a nucleation/growth mechanism, while the deposition of lead was found to be diffusion controlled. The diffusion coefficient calculated for Pb2+ ions in basic melt by voltammetry was in agreement with the deductions of transient method. The analysis of the chronoamperograms indicates that the deposition process of lead on Al substrates was controlled by 3D diffusion control, nucleation and growth. The processes are manifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain the kinetic parameters from the theoretical model proposed for this system. It is found that under more cathodic potential, the saturation number density of the formed lead nuclei and also the efficiency of the use of the available surface nucleation sites increased. The morphology of the aluminum deposits in both the presence and absence of PbCl2 was examined by SEM.
Keywords: Electrocrystallization; Nucleation; Growth; Aluminum; Lead;

Crystal structure and magnetic properties of novel intermetallic compounds in the Er–Cu–Ga system by B. Belgacem; M. Pasturel; O. Tougait; M. Potel; T. Roisnel; R. Ben Hassen; H. Noël (89-95).
Three new ternary gallides have been found in the Er–Cu–Ga ternary system. Their crystal structure, as well as that of the previously reported ErCu0.5Ga1.5, has been refined from single crystal X-ray diffraction data. ErCu2−x Ga x (0.4 ≤  x  ≤ 0.7) crystallizes in the CaIn2 structure-type (space group P63/mmc), ErCu5−x Ga x (0.8 ≤  x  ≤ 2.3) in the CaCu5-type (space group P6/mmm), ErCu12−x Ga x (5.7 ≤  x  ≤ 6.7) in the ThMn12-type (space group I4/mmm) and Er14Cu51−x Ga x (5.5 ≤  x  ≤ 11.0) in the Gd14Ag51-type (space group P6/m). Magnetic measurements show Curie–Weiss paramagnetic behavior down to 2 K for these four phases.
Keywords: Intermetallics; Erbium gallides; Single crystal X-ray diffraction; Magnetic properties;

Effect of substitution of Nd for Mg on the hydrogen storage properties of Mg2Ni alloy by D.H. Xie; P. Li; C.X. Zeng; J.W. Sun; X.H. Qu (96-102).
Hydrogen storage alloys Mg2−x Nd x Ni (x  = 0, 0.1, 0.2, 0.3) were prepared by vacuum induction melting under the protection of high purity helium atmosphere. Their phase structures, morphologies and hydrogen storage properties were intensively studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure composition and temperature (PCT) experiments in the present work. XRD and SEM analysis results show that the Mg–Nd–Ni alloys appear multiphase structures involving Mg2Ni, Nd2Ni7, NdMg12 or Nd5Mg41 and other minor phases. It was found that the alloys exhibited good activation behavior, plateau characteristics, and hydrogen absorption–desorption reversibility and kinetic properties. The substitution of Nd for Mg has improved the hydrogen storage properties of Mg2Ni evidently and kept relative high hydrogen capacities. The pressure composition isotherms (PCIs) of the Mg–Nd–Ni alloys display two plateaus, the lower and narrow ones corresponding to MgH2 formation and the higher and broad ones corresponding to Mg2NiH4 formation. Among the Mg–Nd–Ni alloys, the Mg1.9Nd0.1Ni alloy has the best hydrogen absorption and desorption kinetics, the highest hydrogen capacity and good reversibility.
Keywords: Hydrogen storage; Hydrogen absorption and desorption kinetics; Pressure composition isotherm (PCI); Hydrogen capacity;

Density-functional study of the U–Zr system by Alex Landa; Per Söderlind; Patrice E.A. Turchi (103-110).
Density-functional formalism is applied to study the phase equilibria in the U–Zr system. The obtained ground-state properties of the γ (bcc) and δ (C32) phases are in good agreement with experimental data. The decomposition curve for the γ-based U–Zr solutions is calculated. Our calculations confirm that experimentally observed “partial” ordering of the alloy components in the δ-UZr2 (AlB2) phase, in which Zr atoms occupy the “Al” position and the two “B” sites are randomly shared by the U and Zr atoms, is the most energetically favorable within the C32 structure. We argue that stabilization of the δ-UZr2 phase relative to the α-Zr (hcp) structure is due to an increase of the Zr d-band occupancy that occurs when U is alloyed with Zr. A comparison with stabilization of the ω-phase (also C32) in Zr under compression is made.
Keywords: Nuclear reactor materials; Phase transitions; Computer simulations;

Solute segregation and its influence on the microstructure and electrochemical behavior of Ti–Nb–Zr alloys by D.Q. Martins; M.E.P. Souza; S.A. Souza; D.C. Andrade; C.M.A. Freire; R. Caram (111-116).
The main aim of this work is to evaluate microstructure and electrochemical behavior of Ti–30Nb–xZr alloys using polarization techniques. Several alloys with different Zr contents were evaluated (from 2.5 to 15 wt.%). Samples were prepared by arc melting and cast in copper molds in a centrifugal casting machine. The as-cast samples showed a dendritic microstructure whose scale was found to depend on the Zr content. Martensite formation proved to be dependent on solute segregation. It was observed that the addition of Zr has no influence on corrosion potential. However, Zr addition affects the passive current density behavior. After polarization, the microstructures with passive film formed on their surfaces were analyzed by scanning electron microscopy.
Keywords: Metals; Casting; X-ray diffraction; Electrochemical reactions; Thermal analysis;

Synthesis of Mg–Ti FCC hydrides from Mg–Ti BCC alloys by Kohta Asano; Hirotoshi Enoki; Etsuo Akiba (117-120).
Hydrogenation of Mg–Ti BCC (body centered cubic) alloys which were prepared by means of ball milling has been carried out. Mg–Ti hydride with a FCC (face centered cubic) structure was successfully synthesized under a hydrogen pressure of 8 MPa at 303 K for 270 h and at 423 K for 122 h. The synthesized Mg–Ti FCC hydride phase had a chemical formula and the lattice parameter of Mg42Ti58H177 (H/M = 1.77 or hydrogen content of 4.7 mass%) and 0.449(7) nm, respectively.
Keywords: Magnesium–titanium alloys; BCC phase; Mechanical alloying; Ball milling; Hydrogen storage;

The reactions between Cu and the Sn2.5Ag0.8Cu solders doped with 0.03 wt.% Fe, Co, or Ni were studied. Reaction conditions included multiple reflows for up to 10 times and solid-state aging at 160 °C for up to 2000 h. In the multiple reflow study, Cu6Sn5 was the only reaction product noted for all the different solders used. Reflows using the solder without doping produced a thin, dense layer of Cu6Sn5. Adding Fe, Co, or Ni transformed this microstructure into a much thicker Cu6Sn5 with many small trapped solder regions between the Cu6Sn5 grains. In the solid-state aging study, both Cu6Sn5 and Cu3Sn formed, but adding Fe, Co, or Ni produced a much thinner Cu3Sn layer. Because the Cu3Sn growth had been linked to the formation of micro voids, which in turn increased the potential for a brittle interfacial fracture, thinner Cu3Sn layers might translate into better solder joint strength.
Keywords: Solder; Soldering; Diffusion; Intermetallics;

Kinetics of grain growth in 2024-T3: An aerospace aluminum alloy by Zainul Huda; Tuan Zaharinie (128-132).
The 2024-T3 aerospace aluminum alloy has been characterized and annealed by use of modern material characterization, metallographic and heat treatment equipments. The kinetic equations and the Arrhenius-type equation were applied to compute the grain-growth exponent and the activation energies for grain growth for the investigated alloy at specified temperature. The grain-growth exponent n was computed to be in the range of 0.116–0.121 at temperatures in the range of 250–350 °C (523–623 K). The activation energy for grain growth, Q g, for the investigated alloy has been computed to be 157.1 kJ/mol for the mentioned range of n values. The grain-growth kinetic data for the investigated alloy has been compared with other aluminum and engineering alloys; and analyzed in relation to those reported in recent literature.
Keywords: Metals; Crystal growth; Precipitation; Grain boundaries;

An attempt to understand the rupture creep behavior of aluminum alloy metal matrix composites is made. Data from published investigations on the creep fracture of a variety of materials as well as new data on 6061Al–40 vol% SiCw composite have been analyzed. The analysis is made on the basis of previous studies conducted by these authors in which the relevance of the load partitioning phenomenon was manifested. The well-known phenomenological approach described by the Monkman–Grant equation has been employed. It is seen that the commonly used approximation of n′ = 1 (with n′ the Monkman–Grant exponent) is never satisfied. Rather, n′ < 1 is always obtained. A new form of this equation is proposed in order to understand the creep rupture mechanisms of these materials in greater depth.
Keywords: Metals; Powder metallurgy; High temperature alloys; Creep;

Enhanced grain refinement due to deformation-induced precipitation during ambient-temperature severe plastic deformation of an Al–7%Si alloy by J.M. García-Infanta; S. Swaminathan; C.M. Cepeda-Jiménez; T.R. McNelley; O.A. Ruano; F. Carreño (139-143).
An Al–7wt%Si alloy was prepared by casting. Billets from the as-cast ingot were annealed at 540 °C and then either quenched or furnace cooled to control the Si concentration in the primary Al constituent. Subsequently, as-cast billets as well as billets in the annealed conditions were subjected to ambient temperature severe plastic deformation (SPD) by equal-channel angular pressing (ECAP). Microstructures were evaluated by optical, scanning electron, and transmission electron microscopy methods and Vickers hardness data were also acquired. Grain refinement and hardening in the primary Al by ambient temperature ECAP processing are influenced by deformation-induced precipitation of Si from a supersaturated solid solution. The finest grain size and highest hardness are associated with the greatest initial supersaturation of Si.
Keywords: Equal channel angular pressing (ECAP); Al–Si alloys; Severe plastic deformation; Deformation induced precipitation; Grain refinement;

The complete miscibility gap of fcc solid solution has been obtained by thermodynamic calculation in the Al–Zn–Cu ternary system by means of SSOL data. It is clearly indicated that its shape should be connective tunnel space, transforming continuously from Al–Zn side to Al–Cu side, not bell-shaped space as considered previously. Moreover, it has been also shown that there is metastable miscibility gap of fcc solid solution in Al-rich corner of Al–Cu binary system. Its top temperature is about 500 °C and the corresponding composition is around 13.5 at.% Cu.
Keywords: Al–Zn–Cu system; Miscibility gap; Thermodynamic calculation;

Microstructure and ultrasonic behaviour on thermal heat-treated Al–Li 8090 alloy by V. Rajendran; S. Muthu Kumaran; T. Jayakumar; P. Palanichamy; P. Shankar; Baldev Raj (147-153).
Ultrasonic velocity and attenuation measurements have been carried out on the as-received and thermally treated 8090 Al–Li alloys (T8771). Ultrasonic velocities, density and elastic moduli show a maximum at the thermally treated temperature of 463 K due to the influence of δ′ phase precipitation. The decrease in velocity beyond 463 K is associated with the initiation of dissolution of δ′ and δ phases and also the presence of small fraction of S′ phase. Overaging could be identified at 673 K from the changes in ultrasonic velocities and attenuation. The observed pronounced maxima in ultrasonic velocities and minima in attenuation at 470 and 593 K are associated with precipitation of δ′ and S′ phases, respectively.
Keywords: 8090 Al–Li alloys; Microstructure; Ultrasonic velocity; Attenuation;

The microstructure and mechanical properties of the Al 7075 alloy present in a hot roll-bonded laminate consisting of Al 7075/Al 2024 layers have been characterized by high resolution electron backscattering diffraction (EBSD) analysis and Vickers microhardness, respectively. The as-rolled deformation structure consisted in lamellar bands aligned parallel to the rolling direction. It was found that a post-rolling tempering at 175 °C/6 h, prior to the T6 treatment has a profound effect on the microstructure and the mechanical properties of the Al 7075 alloy. This tempering reduces the driving force for recrystallization during the usual solution treatment of 30 min that is part of the T6 treatment. The performed procedures favour a more homogeneous precipitation during the following age hardening step and the achievement of a noticeable increase in Vickers microhardness.
Keywords: Aluminium alloys; Thermomechanical processing; Microstructure; Mechanical properties; EBSD analysis;

Preparation of the TaC–TaB and TaC–TaB2 composites with a broad range of the phase composition was conducted by self-propagating high-temperature synthesis (SHS) with the samples compressed from the Ta–B4C and Ta–B4C–C powder mixtures. Under a preheating temperature of 200 °C, self-sustaining combustion in the reactant compact was achieved. Experimental results showed that the reaction temperature and propagation velocity of the combustion front depended upon the phase and content of the boride formed in the composite. Higher reaction temperatures and faster reaction fronts were observed in the formation of the composites containing TaB than TaB2. Moreover, due to the higher formation enthalpy for TaB than TaC, the combustion temperature and reaction front velocity increased with TaB content when the TaC–TaB composites were synthesized. However, on account of the larger heat capacity of TaB2 than that of TaC, an opposite trend was observed in the synthesis of the TaC–TaB2 composites. The XRD pattern of the synthesized product confirms SHS formation of the TaC–TaB and TaC–TaB2 composites from the reactions of the Ta–B4C–C and Ta–B4C powder compacts under well-designed stoichiometries.
Keywords: Ceramics; Composite materials; Solid state reaction; X-ray diffraction;

Thermal barrier coating of lanthanum–zirconium–cerium composite oxide made by electron beam-physical vapor deposition by Zhenhua Xu; Limin He; Xinghua Zhong; Rende Mu; Shimei He; Xueqiang Cao (168-172).
Lanthanum–zirconium–cerium composite oxide (La2(Zr0.7Ce0.3)2O7, LZ7C3) as a candidate material for thermal barrier coatings (TBCs) was prepared by electron beam-physical vapor deposition (EB-PVD). The composition, crystal structure, thermophysical properties, surface and cross-sectional morphologies and cyclic oxidation behavior of the LZ7C3 coating were studied. The results indicated that LZ7C3 has a high phase stability between 298 K and 1573 K, and its linear thermal expansion coefficient (TEC) is similar to that of zirconia containing 8 wt% yttria (8YSZ). The thermal conductivity of LZ7C3 is 0.87 W m−1  K−1 at 1273 K, which is almost 60% lower than that of 8YSZ. The deviation of coating composition from the ingot can be overcome by the addition of excess CeO2 and ZrO2 during ingot preparation or by adjusting the process parameters. The failure of the LZ7C3 coating is mainly a result of the occurrence of micro-cracks inside ceramic topcoat, which cause the abnormal oxidation of bond coat.
Keywords: Thermal barrier coatings; EB-PVD; Thermal cycling; La2(Zr0.7Ce0.3)2O7 composite oxide;

Oxidation behavior of AlN–SiC–TiB2 ceramics synthesized by SHS–HIP by Lijuan Zhou; Yongting Zheng; Shanyi Du; Hongbo Li (173-176).
The present study aims to investigate the oxidation behavior of AlN–SiC–TiB2 composites, synthesized by self-propagating high-temperature synthesis (SHS) and hot isostatic pressing (HIP). Oxidation experiments are carried out in the temperature range from 900 °C to 1400 °C for 1–16 h under air atmosphere. The evaluation of the oxidation kinetics and the modification of the microstructure on the exposed surfaces are investigated. The weight gain per unit surface area as a function of time increased parabolically with the oxidation time from 900 °C to 1400 °C and it is accelerated sharply when the temperature is raised up to 1400 °C. The oxidation products on the sample surfaces are mainly constituted of crystalline mullite and titanium oxide.
Keywords: AlN–SiC–TiB2; SHS–HIP; Oxidation; Microstructure;

Characteristics of Sn–Ni alloy powders directly prepared by spray pyrolysis by Seo Hee Ju; Hee Chan Jang; Yun Chan Kang; Dong-Won Kim (177-180).
Fine size Sn–Ni alloy powders with spherical shape were directly prepared by spray pyrolysis. The alloy powders prepared at temperatures below 1200 °C had bimodal size distributions of nano- and submicron-sized powders. Nano-sized powders were formed by chemical vapor deposition process from the evaporated Sn component. The powders had main peaks of Sn–Ni alloys irrespective of the preparation temperatures. Ni and Sn components are well dispersed inside the submicron-sized powders. The initial discharge capacity of the Sn–Ni alloy powders prepared at a temperature of 1100 °C was 477 mAh/g. However, the initial discharge capacity of the Sn–Ni alloy powders prepared at temperature of 1000 and 1200 °C temperature were 255 and 411 mAh/g respectively. The Sn–Ni alloy powders prepared at a temperature of 1100 °C had more good cycle performance than those prepared at temperatures of 1000 and 1200 °C.
Keywords: Chemical synthesis; Gas–solid reaction; Electrode materials; Metals and alloys;

Phase transformation of η and σ phases in an experimental nickel-based superalloy by F. Long; Y.S. Yoo; C.Y. Jo; S.M. Seo; H.W. Jeong; Y.S. Song; T. Jin; Z.Q. Hu (181-187).
Both nodular σ phase and platelet η phase were found in the as-cast microstructure of an experimental nickel-based superalloy. The nodular σ phase decomposed into γ phase leaving serrated transformation interfaces between σ and γ during the heat treatment process. The formation mechanism of nodular σ phase and platelet η phase was investigated by analyzing the orientation relationship of σ/γ and η/γ. It was found that σ phase nucleated and grew from the liquid during solidification in the interdendritic area. The η phase had regular platelet morphology and definite orientation relationship with γ phase, which indicated that it was formed by means of solid-state precipitation.
Keywords: Superalloy; η phase; σ phase; Phase transformation;

Environmental degradation of NdFeB magnets by Gaolin Yan; P.J. McGuiness; J.P.G. Farr; I.R. Harris (188-192).
Keywords: Permanent magnets; Corrosion;

Effect of Ni–Al atomic ratio on glass formation in La–Al–Cu–Ni bulk metallic glasses by Peiyou Li; Shandong Li; Zongjun Tian; Zhigao Huang; Fengming Zhang; Youwei Du (193-196).
Glass forming ability (GFA) and thermal properties were investigated for La62Al14(Cu1−x Ni x )24 (x  = 0.2, 0.4, 0.6 and 0.8) bulk metallic glasses (BMGs). The experimental results show that in the La-based La–Al–(Cu–Ni) pseudo-ternary system, optimum glass formation actually occurs at the Ni:Al ratio of 1:1. It has been found that the GFA is much better in the range of unstable intermetallic compound (AlNi) than that of adjacent stable intermetallic compound (AlNi3). The asymmetry of negative heat of mixing between the atomic pairs of La–Cu and La–Ni, Al–Cu and Al–Ni is also considered as another influencing factor of GFA. It might be an effective way to develop and design BMGs by adjusting the Ni–Al atomic ratio in Al–Ni-contained alloy systems.
Keywords: Bulk metallic glass; Glass forming ability; Atomic ratio;

Thermodynamic assessments of the Co–Er and V–Er systems by C.P. Wang; A.Q. Zheng; X.J. Liu; K. Ishida (197-201).
The Co–Er and V–Er binary systems have been thermodynamically assessed by using the CALPHAD (calculation of phase diagrams) approach on the basis of the experimental data including the thermodynamic properties and phase equilibria. Gibbs free energies of the solution phases (liquid, fcc, bcc and hcp) were modeled by the subregular solution model with the Redlich–Kister formula, and those of the intermetallic compounds (Co17Er2, Co5Er, Co7Er2, Co3Er, Co2Er, Co7Er12 and CoEr3) were described by the sublattice model. A proper set of the thermodynamic parameters has been derived for describing the Gibbs free energies of each phase in the Co–Er and V–Er systems. An agreement between the calculated results and experimental data is obtained.
Keywords: Phase diagrams; Rare earth alloys and compounds; Thermodynamic modeling;

Bulk metallic glass (BMG) composites containing ductile phase were prepared by rapid water quenching of a homogenous Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 melt. The microstructure and composition of the materials were investigated by X-ray diffraction (XRD), optic microscopy (OM), and scanning electrion microscopy (SEM) attached with energy-dispersive spectroscopy (EDS). The secondary dendrite arm spacing (SDAS) in the composites was detected and the solidification parameters of this amorphous composites were obtained. The result shows that the composition of the dendrite phase is depleted in Ni, Cu and enriched in Zr, Nb and Ti, which strongly deviates from the nominal composition. SDAS is gradually increasing from the surface to the centre of the specimen, which inverses proportionally to cooling rate in Newton cooling type. With the increasing diameter of the samples, the secondary arm spacing gradually increases, except the specimen with the diameter of Φ25 mm. Meanwhile, the relationship between SDAS and sample diameter or thickness is given quantitatively.
Keywords: BMG composite; Non-equilibrium solidification; Secondary dendrite arm spacing (SDAS);

Spherical shape Ni–Co alloy powders directly prepared by spray pyrolysis by Hee Chan Jang; Seo Hee Ju; Yun Chan Kang (206-209).
Spherical shape Ni–Co alloy powders were directly prepared by spray pyrolysis in reduction atmosphere. The alloy powders prepared at temperatures of 1000 and 1200 °C had hollow structures and large sizes. On the other hand, the alloy powders prepared at a temperature of 1400 °C had dense structure and fine size. The mean size and geometric standard deviation of the powders prepared at a temperature of 1400 °C were 0.69 μm and 1.5. The BET surface area of the alloy powders prepared at a temperature of 1400 °C was 1.6 m2/g. The composition ratio of Ni and Co components were well coincided with that of the spray solution. The alloy powders had similar saturation magnetization (M s ) values irrespective of the preparation temperatures. However, the coercive force (H c ) values of the alloy powders decreased with increasing the preparation temperatures.
Keywords: Chemical synthesis; Gas–solid reaction; Ceramics;

The interface structures of the (Al2O3  + Al3Zr)/A356 nanocomposites fabricated by magneto-chemistry in situ reaction are investigated by TEM technologies. The results indicate that the Al3Zr/Al, Al2O3/Al and Al2O3/Si interfaces are net and smooth, no interface reactants are observed. The vector relations for Al3Zr and α-Al phases are: [ 2 ¯ 2 ¯ 1 ] A l 3 Zr [ 0 0 1 ] Al , ( 0 1 2 ) A l 3 Zr ( 1 1 ¯ 0 ) Al , and [ 1 ¯ 1 0 0 ] α -A l 2 O 3 [ 1 ¯ 1 1 ] Si , ( 0 0 0 1 ) α -A l 2 O 3 ( 1 1 0 ) Si for α-Al2O3 and Si phases. The misfit degree δ for the (0 0 0 1) crystal plane of the α-Al2O3 phase and the (1 1 0) crystal plane of the Si phase is 5.08%. The interface fit-relations for the Al2O3 phase and the Si phase are that the Si phase can be nucleated on theα-Al2O3 phase. These contribute to the perfect properties of the nanocomposites.
Keywords: Magnetochemistry; Nanocomposites; Interface; Misfit degree;

Thermal and mechanical properties of the Zr53Cu30Ni9Al8 based bulk metallic glass microalloyed with silicon by Jason S.C. Jang; S.R. Jian; C.F. Chang; L.J. Chang; Y.C. Huang; T.H. Li; J.C. Huang; C.T. Liu (215-219).
The amorphous alloy rods of (Zr53Cu30Ni9Al8)100−x Six (x  = 0.25, 0.5, 0.75, 1) with a diameter of 2–6 mm were prepared by drop casting method in an Ar atmosphere. The thermal properties, including glass forming ability (GFA) and thermal stability during isothermal annealing of these amorphous alloys, and the mechanical properties have been systematic investigated by the combination of DSC, XRD, SEM, TEM, and compression test. The result of X-ray diffraction reveals that these entire (Zr53Cu30Ni9Al8)100−x Si x alloy rods exhibit a typical amorphous diffraction pattern with only a broad maximum around 2θ around 40 degree. Both T g (glass transition temperature) and T x (crystallization temperature) of these (Zr53Cu30Ni9Al8)100−x Si x alloys increase with the silicon addition. In addition, both the activation energy of crystallization and the incubation time of isothermal annealing these (Zr53Cu30Ni9Al8)100−x Si x amorphous alloys indicate that the (Zr53Cu30Ni9Al8)99.25Si0.75 alloy possesses the best thermal stability in the (Zr53Cu30Ni9Al8)100−x Si x alloy system. In parallel, the result of compression test shows that the yield strength increases with the addition of Si content and reaches to a maximum value about 1750 MPa with 3% plastic strain for the (Zr53Cu30Ni9Al8)99.25Si0.75 amorphous alloy.
Keywords: Zr-base BMG; Glass forming ability; Thermal stability; Microalloying;

High-temperature oxidation behavior of TiAl-based alloys fabricated by spark plasma sintering by X. Lu; X.B. He; B. Zhang; X.H. Qu; L. Zhang; Z.X. Guo; J.J. Tian (220-225).
Alloys of Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y and Ti–47.5Al–2.0V–1.0Cr have been prepared by spark plasma sintering (SPS). Their high-temperature oxidation behavior at 1000 °C in air has been investigated. The results indicate that the Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y alloy possesses superior oxidation resistance, which is greatly better than that of Ti–47.5Al–2.0V–1.0Cr alloy under the same condition. The enhanced property is mainly attributable to 8.5 at.% Nb addition. For the Ti–47.5Al–2.5V–1.0Cr alloy, the outer oxide scale is dominated by TiO2 with a small amount of Al2O3, and the inner scale consists of many separate alternating Al2O3/TiO2 layers. By comparison, the inner oxide scale of Ti–45Al–8.5Nb–0.2B–0.2W–0.1Y underneath the outer TiO2-rich layer is composed of TiO2 and a minor amount of TiN. Additionally, Nb is found to be enriched at the interface of the oxide scale and the substrate. The addition of Nb promotes the formation of TiN in the oxide scale and Nb-enriched diffusion layer between the scale and the substrate, which is effective to impede the diffusion of Ti and O ions.
Keywords: TiAl alloys; Spark plasma sintering (SPS); High-temperature oxidation; Oxide scales;

Bulk metallic glass (BMG) Fe75Hf3Mo3B15Y4 can be cast into glassy rod with a diameter of at least 2 mm by copper mold casting technique under a low vacuum of 1.5 Pa. The alloy exhibits a large supercooled liquid region of 57 K and high glass transition temperature of 855 K, demonstrating a good thermal stability. Moreover, the as-cast BMG also shows good soft magnetic properties with a high saturation magnetization of 95 emu/g and low coercivity of around 1.4 Oe at room temperature.
Keywords: Metallic glasses; Rapid solidification; Magnetic measurements;

Rutherford backscattering spectroscopy (RBS) technique with computer simulations are developed for numerical analysis of the level-by-level element composition of rapidly solidified foils of the Al–Mn alloy. It has been obtained that the manganese depth distribution in the foils is irregular in the near-surface region of the samples. Thin surface layer (0.03 μm) is impoverished by manganese in a substrate region. Depth-dependent elemental composition of the foils remains constant after annealing at 200 °C. The manganese content of surface layer grows with increasing of annealing temperature. A correlation of dope depth profiles and both phase composition and surface of analysis of the annealed foils is observed.
Keywords: Liquid quenching; Metals; Rutherford backscattering; Microstructure;

Mechanochemical synthesis, thermal stability and selective electrochemical dissolution of Cu–Ag solid solutions by T. Spassov; L. Lyubenova; Y. Liu; S. Bliznakov; M. Spassova; N. Dimitrov (232-236).
Supersaturated nanocrystalline (16–19 nm) Cu50Ag50 and Cu70Ag30 solid solutions are synthesized by high-energy ball milling. Varying the milling time fcc solid solutions with different lattice parameters are obtained. Thus an increase of the lattice constant that levels off after 20 h of milling is registered for the Cu50Ag50 solid solution. At the same time broad overlapped exothermic effects in the temperature range of 170–370 °C are detected by DTA. These can be associated mainly with solid solution decomposition and a grain growth process. Electrochemical selective dissolution reveals a quasi-critical potential of Cu dissolution in Cu70Ag30 that is shifted 40 mV positively, compared to the dissolution potential of pure Cu, thus ascertaining the Cu (Ag) solid solution formation. The linear area development with the in-depth progress of the Cu dissolution front confirms the dealloying applicability for fabrication of nanoporous Ag structures in this case.
Keywords: Cu–Ag alloys; Supersaturated solid solution; Thermal stability; Decomposition; Selective dissolution; Nanoporous structure;

In this paper, a new preparation technology is proposed to manufacture nano-alumina particle-reinforced copper alloy. The new preparation technology includes three processes: mechanical alloy, hydrogen sintering and explosive compaction. The microstructure indicates αAl2O3 particles are dispersed in copper matrix and still keep the nanometer scale. We apply three kinds of explosion pressure, which is 2 GPa, 4 GPa and 6 GPa respectively, to research the influence of explosion pressure on compaction quality. The detection results show that the relative density and hardness of samples increase with the rise of explosion pressure, but diameter of Mach hole increase thereupon too. The most suitable explosion pressure for Cu/αAl2O3 mixed powder is 4 GPa under the pressure the sample's relative density reaches 98.61% and hardness reaches 112 HV.
Keywords: Nanostructured materials; Powder metallurgy; Mechanical alloying; Microstructure; High-pressure;

The microstructure evolution of Ni-25 at.% Al thin films prepared by magnetron co-sputtering is investigated by using in-situ transmission electron microscopy (TEM) study from room temperature to 750 °C. The diffraction rings of both Ni and Al are present in the selected area electron diffraction (SAED) of as-deposited films, and then the diffraction ring of Al disappears when the films are heated up to 300 °C. At 500 and 700 °C, the diffraction rings and spots of L12 intermetallic Ni3Al phase are found, respectively, which means that the formation of ordered Ni3Al phase starts from 500 °C. Moreover, it is found that the grain growth is relatively slow when the temperature is lower than 300 °C, while all of normal grain growth, abnormal grain growth and annealing twinning occur at higher temperatures.
Keywords: Intermetallics; Thin films; Transmission electron microscopy;

Mechanical alloying and reactive milling in a high energy planetary mill by Xianjin Jiang; Mikhaylo A. Trunov; Mirko Schoenitz; Rajesh N. Dave; Edward L. Dreizin (246-251).
Powder refinement in a planetary mill (Retsch PM 400-MA) is investigated experimentally and analyzed using discrete element modeling (DEM). Refinement is defined as the average size of the individual components in a composite powder. The specific milling dose, defined as the product of charge ratio and milling time, is used as an experimental parameter tracking the progress of the material refinement. This parameter is determined experimentally for milling of boron and titanium powders, for which the time of initiation of a self-sustained reaction is measured under different milling conditions. It is assumed that the reaction becomes self-sustaining when the same powder refinement is achieved. The DEM calculations established that the milling balls primarily roll along the milling container's perimeter. The inverse of the rate of energy dissipation resulting from this rolling motion is used as the DEM analog of the specific milling dose. The results correlate well with experimental observations.
Keywords: Mechanical alloying; Mechanical milling; Modeling; Simulation;

Solidification of undercooled Ag–Cu eutectic alloy with the Sb addition by Su Zhao; Jinfu Li; Li Liu; Yaohe Zhou (252-256).
The Ag–28.1 wt.%Cu alloy without or with a minor addition (0.5 or 1 wt.%) of Sb was undercooled and spontaneously solidified in the encasement of a glass flux. A non-steady-state radial growth from the nucleation site on the sample surface results in two types of structures, anomalous eutectics near the nucleation site and lamellar eutectics in the other part. The large thermal diffusion coefficient of the Ag–Cu eutectic alloy melt and the relatively slow growth velocity should be responsible for the non-steady-state growth. After a little Sb is added, the solidification interface changes from a cellular morphology into a cellular dendrite and then an undeveloped dendrite, and the tip radius decreases. Correspondingly, the recalescence degree and the recalescence rate increase and the granular particles in the anomalous eutectics become larger because the solidification deviates significantly from the equilibrium state.
Keywords: Metals and alloys; Crystal growth; Rapid-solidification; Microstructure;

Synthesis and characterization of TiAl/α-Al2O3 nanocomposite by mechanical alloying by N. Forouzanmehr; F. Karimzadeh; M.H. Enayati (257-259).
TiAl/α-Al2O3 nanocomposite was synthesized by mechanical alloying of the Al and TiO2 powder mixture. The powder particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the mechanochemical reaction between Al and TiO2 gradually took place through intermediate stages during milling, resulted in the formation of disordered fcc-TiAl and Al2O3 phases. The in situ processing involved two steps in which diffusion of Ti into Al is prominent. Annealing of milled product led to transition of metastable fcc-TiAl into equilibrium γ-TiAl. The crystallite size of phases in produced nanocomposite powder estimated to be about 50 nm.
Keywords: Titanium aluminide; Nanocomposite; Mechanical alloying;

Thermal stability and structural changes during heat treatment of nanostructured Al2024 alloy by M. Jafari; M.H. Enayati; M.H. Abbasi; F. Karimzadeh (260-264).
Thermal stability and structural changes during isothermal heat treatment of nanostructured Al2024 alloy prepared by mechanical milling (MM) were investigated. Al2024 powders were subjected to high-energy milling for various times to produce nanostructured alloy. Nanostructured Al2024 alloy was subsequently annealed at 150–550 °C for 1–3 h under argon atmosphere. The as-milled and annealed powders were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that after 30 h of milling, an Al–Cu–Mg supersaturated solid solution with a grain size of 30 nm was obtained. This structure was then isothermally heat-treated at various temperatures for different times. The CuAl2 and CuMgAl2 precipitates formed after heat treatment at T  < 350 °C. In contrast to CuAl2 phase, CuMgAl2 precipitates disappeared on XRD traces taken after annealing at temperatures higher than 350 °C. Investigation of grain growth kinetics showed that nanostructured Al2024 had high thermal stability so that Al grain size remained in nanosized scale (about 70 nm) even after heating at 550 °C for 3 h. The value of grain growth exponent and activation energy at different annealing temperatures were obtained and discussed in terms of solute and second phase drag effects.
Keywords: Nanostructures; High-energy ball milling; Precipitation;

The response to thermal exposure of mixed and ball-milled Al/K2TiF6 powder blends was investigated in an effort to explore the potential of powder metallurgy processing in the production of Al–Ti alloys. K2TiF6 reacts with aluminium in the solid state, producing Al3Ti and the inorganic salts, KAlF4 and K3AlF6. This reaction which occurs shortly before the melting of aluminium when K2TiF6 and aluminium powders are merely mixed, starts as early as 220 °C when the two powder components are ball-milled before thermal exposure. Heating ball-milled Al/K2TiF6 powder blends in an inert atmosphere for 1/2 h at approximately 500 °C suffices to produce a very fine dispersion of Al3Ti particles inside aluminium grains. The alloy powder thus obtained can be compacted to manufacture Al–Ti pellets which can be employed for grain refining aluminium alloys.
Keywords: Metals; Powder metallurgy; Thermal analysis; Al–Ti alloy;

Age hardening of the Al0.3CoCrFeNiC0.1 high entropy alloy by Tao-Tsung Shun; Yu-Chin Du (269-272).
In this study, an Al0.3CoCrFeNiC0.1 high entropy alloy was synthesized by induction melting in air. The as-cast alloy was heat treated for 5–72 h at 600–1000 °C to investigate the effects of age treatments on the hardness and microstructure. The microstructure of the as-cast alloy consisted of a FCC solid solution matrix and an eutectic k 1 carbide. This k 1 carbide decomposed to a k 2 carbide after being aged at 800–1000 °C. The optimal age hardening occurred at 700 °C, and the hardening effect decreased with further increase in temperature. The precipitation of fine k 2 carbides in the matrix during 700–1000 °C aging is the main age hardening mechanism. In addition, the precipitation of a Ni–Al rich phase at 800 °C and 900 °C provides a secondary hardening effect.
Keywords: Precipitation; Crystal structure; Enthalpy; Microstructure;

A powder metallurgy approach for the production of a MgH2–Al composite material by Alexander Glage; Riccardo Ceccato; Ivan Lonardelli; Fabrizio Girardi; Filippo Agresti; Giovanni Principi; Alberto Molinari; Stefano Gialanella (273-280).
This research work presents a powder metallurgy (PM) route for the production of a hydrogen storage MgH2–Al composite material. This system has been considered to avoid one of the main problems of bulk materials for chemical hydrogen storage, that is decrepitation. The process involves several steps, like cryomilling of pure Al, mixing with MgH2and compaction of the powder blends by Spark Plasma Sintering (SPS). The first part of the work was focused on the optimization of the aluminum scaffold. Cryomilling of aluminum was carried out in order to reduce the crystallite size to the range of nanometers. Pure aluminum specimens were sintered with two different sets of sintering parameters in order to investigate their effect on the properties of the matrix material after the sintering process. Then, a bulk composite consisting of MgH2 and 20 wt.% Al was produced in order to evaluate the resistance to decrepitation. In spite of the comminution of the MgH2 particle size after three hydrogen absorption/desorption cycles, the overall structure is faultless due to the reinforcement introduced by aluminum. Furthermore, aluminum retained its nanocrystalline character during temperature cycling. However, the sample during absorption/desorption cycling showed a reduced hydrogen storage behavior, caused by the formation of the highly stable intermetallic phase Mg17Al12 as well as by a partial oxidation of Mg.
Keywords: Hydrogen absorbing materials; Metal hydrides; Nanostructured materials; Powder metallurgy; Mechanical alloying;

Al based alloys (Al–0.1 wt.%Ti, Al–0.5 wt.%Ti and Al–2 wt.%Li) were prepared using metals of 99.99% high purity in the vacuum atmosphere. These alloys were directionally solidified upward with the different temperature gradients, G, at a constant growth rate, V, and also with the different V at a constant G in the directional solidification apparatus. Cellular spacing, λ, and microindentation hardness, HV, were measured from both transverse and longitudinal sections of the specimen as a function of solidification processing parameters (G, V and cooling rate, T ˙ ) . Dependency of microindentation hardness on the solidification processing parameters and cellular spacing (λ) in the directionally solidified aluminum alloys were experimentally investigated and the relationships between the solidification processing parameters and microindentation hardness, and cellular spacing and microindentation hardness were obtained by linear regression analysis. The results obtained in this work have been compared with the previous similar experimental results obtained for binary alloys.
Keywords: Metals and alloys; Microstructure; Mechanical properties;

Phase equilibria in the Cu–Cr–Nb and Cu–Cr–Co systems were, respectively, determined by metallography, X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray (SEM–EDX) techniques. The thermodynamic assessments of the Cu–Cr–Nb and Cu–Cr–Co systems were carried out by using CALPHAD (CALculation of PHAse Diagrams) method on the basis of the experimental data measured by the present and previous works. The Gibbs free energies of the liquid and solid solution phases were described by the subregular solution model, and those of intermetallic compounds were described by the sublattice model. A consistent set of the thermodynamic parameters has been obtained, and the evaluated thermodynamic parameters lead to a better fit between calculated results and experimental data in both the Cu–Cr–Nb and Cu–Cr–Co systems.
Keywords: Phase diagrams; Transition metal alloys and compounds; Thermodynamic modeling;

Elastic stability, electronic structure and optical properties of PtN2 with pyrite and fluorite structures by N. Bettahar; S. Benalia; D. Rached; M. Ameri; R. Khenata; H. Baltache; H. Rached (297-302).
We present the results of a theoretical study of the structural and optoelectronic properties of PtN2, using the full-potential linearized muffin-tin orbital method (FP-LMTO). In this approach, the local density approximation (LDA) is used for the exchange correlation potential. The calculated total energy allowed us to investigate several structural properties in particular the lattice constant, bulk modulus, pressure derivative of bulk modulus. The phase stability was determined from total energy calculations for both the pyrite (C2) and fluorite (C1) phases. A numerical first-principles calculation of the elastic constants was used to calculate C 11, C 12 and C 44. We estimated the Debye temperature of PtN2 from the average sound velocity. Band structure, density of states, band gap pressure coefficients and effective masses are also given. On the other hand, an accurate calculation of linear optical functions (the dielectric function, refraction index and reflectivity R(ω)) is performed in the photon energy range up to 13.5 eV. The results obtained are compared with other calculations and experimental measurements.
Keywords: Ground states; Electronic properties; Optical properties; Elastic constants;

Dependence of anisotropy and coercivity on microstructure in HDDR Nd–Fe–B magnet by M. Liu; Y. Sun; G.B. Han; W. Yang; R.W. Gao (303-307).
The effect of microstructure on the anisotropy and the coercivity in HDDR Nd–Fe–B magnet has been investigated by putting forward a theoretical anisotropy model influenced simultaneously by both the structure defect and the exchange coupling interaction. The results showed that the coercivity is greatly influenced by both the defect thickness, r 0, and the anisotropy constant, K 1(0), at grain surface. Coercivity is determined by the pinning mechanism when K 1(0) ≤ 0.4K 1 and r 0  < 4 nm or K 1(0) > 0.4K 1. However, it is controlled by the nucleation mechanism when K 1(0) ≤ 0.4K 1 and r 0  > 8 nm. For all values of K 1(0), the coercivity first increases, reaches the maximum and then decreases with increasing r 0, and its maximum value decreases with increasing K 1(0). The maximum coercivity is 1102 KA/m while K 1(0) = 0 and r 0 is close to the thickness of domain wall (∼4 nm), which is consistent with experimental results given by other authors.
Keywords: HDDR Nd–Fe–B magnet; Microstructure; Anisotropy; Coercivity;

The hydrogen storage properties of a magnesium-rich Mg–Ni–La alloy prepared by melt-spinning are significantly improved by nanostructure formation during crystallization and activation. It can absorb and desorb ∼5 wt% hydrogen at temperatures as low as 200 °C in moderate time periods. Transmission electron microscopic (TEM) studies on this alloy indicate that the nanostructure, consisting of LaH3 and Mg2NiH4 nano-particles dispersed homogeneously in MgH2 matrices after hydrogenation, is rather stable at temperatures below 300 °C but undergoes coarsening and segregation of these particles and matrices above ∼400 °C. These structural changes have been confirmed by electron energy-loss spectroscopic (EELS) imaging as well as high-resolution TEM techniques. A new EELS peak associated with a plasmon excitation in the MgH2 phase (H-plasmon) is found for the first time in this study. By imaging the H-plasmon peak, the hydrogen distribution in the alloy has been clearly visualized. We have succeeded in observing the hydrogen desorption process at ∼400 °C in-situ in the microscope using this EELS imaging technique.
Keywords: Hydrogen; Mg–Ni–La alloy; Nanostructure; TEM; EELS; H-plasmon; TDS;

The growth process of rod-shaped La0.7Sr0.3MnO3 in solid state method by Shuyan Qi; Jing Feng; Xiaodong Xu; Jingping Wang; Xiangyu Hou; Milin Zhang (317-320).
The rod-shaped La0.7Sr0.3MnO3 (LSMO) nanorods are prepared by a simple solid-state route, in which KMnO4 and MnCl2 are used as raw materials to prepare the precursor of MnO2 fibres. The diameter of as-obtained LSMO rods is about 50 nm and their length longer than 10 μm. We found that there is a close relation between morphology and the conditions of synthesis for LSMO preparing by MnO2 fibres as seeds. The process of the rods growth is observed by calcining the samples at different temperatures and periods of time. In the rods growth process, many small aggregates formed containing large numbers of rods in a low temperature (lower than 950 °C). These aggregates then broke up to form a large number of individual LSMO rods (950 °C, 5 h). Finally, the rods changed into cubic particles with prolonging treatment time to more than 5 h at 950 °C.
Keywords: Perovskite; Solid state method; Rod shape; Seed growth method;

Atomic packing efficiency and phase transition in a high entropy alloy by F.J. Wang; Y. Zhang; G.L. Chen (321-324).
With the increasing of Al content in a high entropy alloy of Ti0.5CrFeCoNiAl x Cu1−x , the phase structure of face centered cubic (FCC) transits to body centered cubic (BCC), namely from a structure with high atomic packing efficiency (APE) to a lower one, and the compressive strength increases from 1650 MPa to 2697 MPa. The phase transition and the strength increases are explained by the lattice distortion.
Keywords: High entropy alloy; Atomic packing efficiency; Strength;

Plasma-activated nitrogen-doped p-type ZnO thin films with multi-buffer-layers grown on sapphire (0 0 0 1) by L-MBE by Dong Wang; Jingwen Zhang; Yunpeng Peng; Zhen Bi; Xuming Bian; Xin’an Zhang; Xun Hou (325-329).
Nitrogen-doped ZnO (ZnO:N) thin films with multi-buffer-layers, Mg0.1Zn0.9O / ZnO super-lattice structure, were grown on sapphire (0 0 0 1) by plasma-activated laser molecular beam epitaxy (L-MBE) using an atomic nitrogen source. High resolution X-ray diffraction (HR-XRD) measurement demonstrated that all the ZnO:N samples are (0 0 0 2) oriented and the residual strain along c-axial are effectively controlled. Room temperature (RT) Hall measurements indicate that the 200 °C sample shows a p-type behavior with a mobility of 4.08 cm2/V s and a carrier density of 1.47 × 1 0 17  cm−3. The 300 °C sample shows a weak p-type behavior with a mobility of 0.75 cm2/V s and a carrier density of 4.40 × 1 0 16  cm−3. However, the 200 °C sample is not stable and reverted back to n-type conductivity in about 5 days. The X-ray photoelectron spectra (XPS) of N1s display two peaks at 404 eV and 396 eV which are related to (N2)Oand NO, respectively. The 10 K low temperature photoluminescence (PL) spectra of the 200 °C sample exhibits an acceptor bound exciton peak at 3.351 eV and a donor–acceptor pair (DAP) peak at 3.228 eV, associated with NO acting as acceptors.
Keywords: Oxide materials; Semiconductors; Impurities in semiconductors; Optical spectroscopy;

Influence of nickel thickness on the properties of ITO/Ni/ITO thin films by J.H. Park; J.H. Chae; Daeil Kim (330-333).
ITO single-layer and ITO/Ni/ITO (INI) multilayer films were deposited by reactive magnetron sputtering on unheated polycarbonate (PC) substrates. The influence of the Ni interlayer on the structural and optoelectrical properties of the film composite was investigated by keeping the thickness of ITO and INI films at 100 and 50/5/45 nm, respectively.Deposited ITO and INI films had an optical transmittance at a wavelength of 550 nm of 84% and 73% by discounting the PC substrate, respectively, while INI films exhibited a resistivity 10 times lower than that of ITO films (3.2 × 10−4  Ω cm vs. 3.0 × 10−3  Ω cm, respectively). XRD diffraction patterns demonstrated that the deposited ITO films had In2O3 diffraction peaks at (1 0 0) and (2 2 2). In contrast, INI films did not have any diffraction peaks. Surface morphology also appeared to influence the Ni interlayer. Specifically, INI films exhibited a lower root mean square (RMS) roughness of 0.5 nm compared with ITO films, which had RMS roughness of 2.1 nm. The figure of merit reached a maximum of 1.3 × 10−3  Ω−1 for INI films which is greater than that of ITO films (0.5 × 10−3  Ω−1).
Keywords: Thin films; Optical properties; Atomic force microscopy; X-ray diffraction;

The transformation characteristics from the austenite to bainite in a 30CrNi3MoV steel were systematically investigated in the continuous cooling rate range of 5–20 °C/min by high-resolution dilatometric measurements and microstructural observations. According to the kinetic information obtained from dilatometric measurements, it is recognized that the bainitic transformation in the explored 30CrNi3MoV steel exhibits not only incompleteness but also stasis features. Microstructure analysis suggests that carbon-rich austenite is retained after the bainitic transformation (normally termed as bainitic incompleteness), and it further evolves into the twin martensite with high-carbon content when the applied cooling rate is above 8 °C/min. The retained austenite will be reserved permanently when the applied cooling rate is as slow as 5 °C/min. The incompleteness of bainitic transformation is believed to be benefit for the further improvement of mechanical properties due to the presence of short twin martensite plates among the lower bainites.
Keywords: Metals; Thermal analysis; X-ray diffraction;

A core-shell like composite In2O3@Ba2In2O5 was synthesized via a novel chemical impregnation method with sample calcination temperatures varying from 600 °C to 1000 °C. Crystal structure, phase transformation, and surface morphology due to heat treatment were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), respectively. Additionally, in order to test the photocatalytic activity of the composite, the samples were added to a methylene blue (MB) solution, exposed to visible light, and then characterized by UV–vis diffused reflectance spectroscopy. Based on the XRD patterns, it could be determined that as calcination temperature was increased from 600 °C to 1000 °C, the outer shell of the composite transformed from Ba4In6O13 to Ba2In2O5 and from Ba2In2O5 to BaIn2O4. The composite sample synthesized with a Ba/In mole ratio of 0.9 and a calcination temperature of 800 °C demonstrated the best photocatalytic degradation activity out of all composite samples calcined at various temperatures. It degraded 100% of the MB in 30 min compared with commercial TiO2 (P-25), which degraded 100% of the MB in 120 min. It is hypothesized that the reason the core-shell like composite experiences superior photocatalytic degradation activity is due to the difference in the composite's energy bands, which drives electron–hole separation when light hits the core-shell like composite.
Keywords: Composite materials; Chemical synthesis; Catalysis; X-ray diffraction; TEM;

Comprehensive studies of the relative effects of dilute alloying elements on the electrical conductivities of metals and alloys have been conducted by developing an effective pattern recognition application. In particular, the effects of 79 elements on three most commonly used metals of copper, aluminum and steel are reported. Our model offers a practical tool to predict the trends of changes in electrical conductivity of any host metal undergoing single or multinary element alloying. It covers not only the elements for which the Norbury–Linde rule is valid but any elements in the periodic table. Furthermore, it is found that the effects of elements of the same group in the period table normally reduce as the increment in the periods. Consequently, our model provides new information and knowledge for the design of alloys of either good electrical conductivity or high resistivity.
Keywords: Metals and alloys; Electrical transport; Computer simulations;

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs), a stable proton-conducting La0.99Ca0.01NbO4 (LCN) thin electrolyte was fabricated on a porous NiO–La0.5Ce0.5O1.75 (NiO–LDC) anode by in situ screen printing. The key part of this process is to directly print well-mixed ink of La2O3, CaCO3 and Nb2O5 instead of pre-synthesized LCN ceramic powder on the anode substrate. After sintering at 1400 °C for 5 h, the full dense electrolyte membrane in the thickness of 20 μm was obtained. A single cell was assembled with (La0.8Sr0.2)0.9MnO3−δ –La0.5Ce0.5O1.75 (LSM–LDC) as cathode and tested with humidified hydrogen as fuel and static air as oxidant. The open circuit voltage (OCV) and maximum power density respectively reached 0.98 V and 65 mW cm−2 at 800 °C. Interface resistance of cell under open circuit condition was also investigated.
Keywords: Solid oxide fuel cells; Ca-doped LaNbO4; Proton-conducting electrolyte; Screen printing; In situ reaction;

The columnar to equiaxed transition during the horizontal directional solidification of Sn–Pb alloys by José N. Silva; Daniel J. Moutinho; Antonio L. Moreira; Ivaldo L. Ferreira; Otávio L. Rocha (358-366).
Experiments have been carried out to analyze the columnar to equiaxed transition during the horizontal directional solidification of Sn–Pb hypoeutectic alloys as a function of solidification parameters, heat transfer coefficients, temperature gradients, growth rates, cooling rates and composition Co. For this purpose, a water-cooled solidification experimental apparatus was developed, and specimens were solidified under unsteady state heat flow conditions. A combined theoretical and experimental approach is developed to quantitatively determine the solidification thermal variables considered. The results have supported a criterion proposed based on a critical value of cooling rate which for a particular binary alloy system is independent of the solute concentration in the hypoeutectic range. The observation of the macrostructures has indicated that the columnar-to-equiaxed transition occurred in a zone rather than in a sharp plane parallel to the chill wall and that resulting thermo-solutal convection seems to favor the structural transition which occurs for a critical cooling rate of about 0.048 K/s and temperature gradients in the range between 0.25 and 0.90 K/mm for any of four alloy compositions examined. A comparative analysis between some results of this work and those from the literature proposed to analyze the CET during upward and downward vertical solidification of Sn–Pb hypoeutectic alloys is conducted.
Keywords: Columnar to equiaxed transition; Horizontal directional solidification; Unsteady-state; Sn–Pb alloys;

Effects of annealing temperature on the structural and optical properties of ZnO hexagonal pyramids by E. Bacaksiz; S. Yılmaz; M. Parlak; A. Varilci; M. Altunbaş (367-370).
ZnO thin films were deposited on quartz substrate at 550 °C by using spray pyrolysis method and subsequently annealed between 600–900 °C with a step of 100 °C. The characterizations of the structural and optical properties of the films have been carried out by means of X-ray diffraction, scanning electron microscopy (SEM) and optical transmittance measurements. XRD ans SEM images indicated that annealing temperature did not play a great role on the microstructure of ZnO films. ZnO thin films are all in hexagonal crystallographic phase and have (0 0 2) preferred orientation, regardless of the annealing temperature. However, SEM studies showed that there exist a high density of micro-rods in the shape of hexagonal pyramid with the width in the order of about 1 μm and height in range of 1–3 μm and the adjacent hexagonal crystals to start fusing with each other along their boundaries at high temperatures. As a result of the optical measurements, it was observed that the films show the low transmittance and optical band gap decreases from 3.15 to 3.10 eV with the increasing of the annealing temperatures up to 800 °C and followed by an increase to 3.20 eV upon further annealing at 900 °C.
Keywords: Zinc oxide; Spray pyrolysis; Transmittance;

Nickel/carbon nanofibers composite electrodes as supercapacitors prepared by electrospinning by Jian Li; En-hui Liu; Wen Li; Xiang-yun Meng; Song-ting Tan (371-374).
Nickel-embedded carbon nanofibers were prepared by the processes of stabilization and carbonation after electrospinning a mixture solution of nickel acetate and polyacrylonitrile in N,N-dimethylformamide. The surface morphology and structure of composites were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD). Compared with performances of composite electrodes with different mass ratios of nickel and carbon by cyclic voltammetry (CV) and chronopotentiogram test, the results show that the introduction of a proper proportion of nickel into carbon could enhance both specific capacitance (SC) and electrochemical stability. The specific capacitance of the carbon nanofiber electrode without the Ni loading was 50 F/g, while that of 22.4 wt.% Ni/carbon electrode increased to 164 F/g. The improved specific capacitance may be attributed to synergic effects from each pristine component, and the electrochemical catalysis effect of nickel.
Keywords: Electrospinning; Ni/C composite; Nanofibers; Supercapacitors;

The ferrite compositions Mg0.80−x Cu0.20Zn x Fe2O4 with x  = 0.5, 0.55, 0.60 and 0.63, were synthesized through nitrate–citrate gels auto-combustion method. The autocatalytic nature of the combustion process has been studied by thermal analysis (DTA and TG) of the dried gels. The as-burnt powders were calcined at 800 °C for 1 h and then pressed ferrite parts were sintered at 900 °C for 4 h. The as-burnt powders and calcined powders were characterized with respect to phase identification, grain size and lattice parameter determination using X-ray diffraction. The sintered ferrites have been investigated for their electrical and magnetic properties such as saturation magnetization, initial permeability, AC-resistivity, dielectric constant, dielectric loss tangent as a function of zinc content. The initial permeability, saturation magnetization, dielectric constant and dielectric loss were found to increase and AC-resistivity was decreased with Zn substitution for Mg. The powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.
Keywords: Ceramics; Sol–gel processes; Magnetization; Dielectric response; Magnetic measurements;

A new ternary Bi-based lead-free piezoelectric ceramic system with perovskite structure (1 −  x  −  y)Bi0.5Na0.5TiO3xBi0.5K0.5TiO3yBiCrO3, was prepared by a conventional solid-state reaction method and the effect of amount of Bi0.5K0.5TiO3 and BiCrO3 on microstructure and electrical properties of the ceramics was investigated. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x  = 0.18–0.21, y  = 0–0.02. And an obvious second phase was observed in the samples with y  = 0.025 and x  = 0.24. The addition of BiCrO3 caused an insignificant promoted grain growth and Bi0.5K0.5TiO3 suppressed the growth of grain. The dielectric constant ɛ r decreases and dielectric loss tan  δ increases with the increase frequency. The optimum piezoelectric properties were obtained near the composition of the MPB. The piezoelectric constant d 33 and the electromechanical coupling factor k p show maximum values of d 33  = 168 pC/N and k p  = 0.32 at x  = 0.18, y  = 0.015 and x  = 0.18, y  = 0.01, respectively.
Keywords: Sodium bismuth titanate; Piezoelectricity; Perovskite structure;

Thermal shock behavior of ZrB2–SiC ultra-high temperature ceramics with addition of zirconia by Weijie Li; Yong Zhang; Xinghong Zhang; Changqing Hong; Wenbo Han (386-391).
Thermal shock behavior of ZrB2–10 vol%SiC ultra-high temperature ceramics with addition of ZrO2 was investigated by means of water-quenching as well as the finite element analysis. Optimal residual strength and critical temperature difference were obtained from ZrB2–10 vol%SiC ceramic added by 10vol%ZrO2. Simulated results revealed that ZrB2–10 vol%SiC–10 vol%ZrO2 provided the lowest thermal stress and stress intensity factor during thermal shock, which confirmed the experimental data. Such improvement in thermal shock resistance compared with ZrB2–10 vol%SiC was primarily ascribed to the improved toughness by the addition of ZrO2. Besides, appropriate phase transformation of ZrO2 during quenching was further beneficial to resist the thermal shock.
Keywords: Ceramics; Microstructure; Phase transitions; X-ray diffraction;

Reaction of titanium with carbon in a laser heated diamond anvil cell and reevaluation of a proposed pressure-induced structural phase transition of TiC by Björn Winkler; Erick A. Juarez-Arellano; Alexandra Friedrich; Lkhamsuren Bayarjargal; Jinyuan Yan; Simon Martin Clark (392-397).
The formation of cubic TiC x from the elements was studied in a laser-heated diamond anvil cell at pressures up to 26 GPa. Annealed samples at these pressures show no splitting of the cubic (1 1 1) or (2 2 2) reflection. This is in contrast to an earlier study, in which a splitting of the (1 1 1) reflection was observed above 18 GPa. The recovered sample had a lattice parameter of 4.3238(6) Å, which implies that the synthesis gave fully stoichiometric TiC. Density functional theory-based model calculations were used to study the dependence of the total energy of a rhombohedral distortion. In these model calculations the total energy was minimal for the undistorted (cubic) lattice. Therefore, the results obtained here imply that at least for titanium carbides with a high carbon content no pressure-induced structural phase transition up to at least 26 GPa occurs. The appearance of a trigonal TiC x polymorph during the synthesis is discussed in terms of its relative stability with respect to the cubic phase.
Keywords: Laser heated diamond anvil cell; Titanium carbide; Phase transition; Density functional theory;

Layered and polycrystalline K2−x Na x Ti4O9 (0.05 ≤  x  ≤ 0.15) ceramics prepared using oxide mixing process have been investigated for their dielectric-spectroscopy. X-ray diffractograms (XRD) show the formation of these compounds in an orthorhombic crystal system with lattice constants evaluated. A schematic model has been proposed for the crystal structure of these compounds. While dielectric losses are attributed to strong dipole mechanism, space charges and electrical conduction, ɛ r (T) plots reveal a sharp transition at 598 K for x  = 0.15 composition which indicates some structural transition involving free dipoles. This may be credited to the ferroelectric to ferroelectric phase transition since increase in the unit cell volume destabilizes the paraelectric phase and boosts the possibility of another ferroelectric phase after transition. Moreover, relative permittivity and loss tangent values categorize them as ‘medium permittivity ceramics’.
Keywords: Ceramics; Solid-state reactions; Crystal structure; Dielectric response; X-ray diffraction;

Preparation of single crystal CuAlNiBe SMA and its performances by Ming Zhu; Xiaosu Ye; Chonghe Li; Gaofeng Song; Qijie Zhai (404-410).
A novel quaternary CuAlNiBe shape memory alloy (SMA) Cu–11.5Al–3.8Ni–0.4Be (wt%) was designed and synthesized in this study. The single crystal of this alloy was fabricated by means of a high temperature gradient directional solidification furnace with a selective growing crystallizer. After solid solution treatment, the phase transformation points (including M s, M f, A s and A f) were determined by DSC; the bending shape memory performance, the maximal recoverable deformations, the tensile strength and the elongation percentage were measured. Its maximum recoverable strain reached 10% which approximately equals to or exceeds the reported maximum recoverable strain for polycrystalline TiNi alloy. The number of bend-relaxing times arrived at 750. Both results implied that this single crystal alloy may become a promising candidate to challenge TiNi SMA.
Keywords: CuAlNiBe; Shape memory alloy; Unidirectional solidification; Single crystal; Mechanical property;

Preparation of silicate stalagmite from sodium silicate by Yong Chen; Yuzhen Hong; Fubing Zheng; Jianbao Li; Yiwen Wu; Ling Li (411-414).
Silicate stalagmites were prepared by a novel approach using sodium silicate as the silica source. Through the reaction of calcium carbonate (CaCO3) with aluminum chloride solution, the produced CO2 gas acted as both reactant and transport gas to carry aluminum ions (Al3+). These Al3+ along with CO2 reacted with sodium silicate resulting in stalagmite growth in solution. The stalagmites obtained were in the range of 15 μm to 2 mm in diameter and 5 cm in length. The growth mechanism is also discussed.
Keywords: X-ray diffraction; Amorphous materials; Chemical synthesis;

Amorphous α-nickel hydroxide was successfully synthesized by rapid freezing micro-emulsion precipitation method. The structure and property of the amorphous α-nickel hydroxide were characterized by XRD, TEM, IR, Raman spectra, and thermal gravimetric analysis. The results of the IR spectroscopy and thermal gravimetric analysis indicate that the amorphous α-nickel hydroxide contains water molecules and anions. Raman spectrum displays more peaks, indicating the highly disordered feature of the amorphous α-nickel hydroxide. Cyclic voltammogram and charge/discharge tests show that the amorphous α-nickel hydroxide in alkaline media has a relatively high discharge capacity (350 mAh g−1) and good structural stability, which indicates its potential application as an electrode material for secondary alkaline batteries.
Keywords: Amorphous material; Nickel hydroxide; Electrode material; Discharge capacity;

Comparative investigations on the microstructures, thermal stability and mechanical properties of Mg77Cu12Zn5Y6 and Mg77Ni12Zn5Y6 bulk metallic glass matrix composites were carried out by using scanning electron microscopy (SEM), DSC and compressive tester. The results show that the microstructure of as-cast samples with 3 mm in diameter for Cu-containing alloy is consisted of Mg flakes and dotted Mg2Cu phase in the amorphous matrix, while the as-cast Ni-containing alloy with the same diameter is mainly consisted of Mg flakes in the amorphous matrix. The glass transition temperature and supercooled liquid region are 413 K and 27 K for the Cu-containing, 443 K and 32 K for the Ni-containing amorphous matrix composites, respectively. The fracture strength, yield strength and plastic strain are 532 MPa, 390 MPa and 2.4% for the Cu-containing alloy, 667 MPa, 412 MPa and 7% for the Ni-containing alloy, respectively. Furthermore, the fracture mechanism for the amorphous matrix composites was discussed according to both the fracture surfaces and the stress–strain curves.
Keywords: Thermal stability; Mechanical properties; Amorphous matrix composites; Fracture mechanism;

Growth and spectral properties of Yb3+-doped Li3Ba2Y3(MoO4)8 crystal by Mingjun Song; Guojian Wang; Lizhen Zhang; Zhoubin Lin; Guofu Wang (423-426).
This paper reports the growth and spectral properties of Yb3+:Li3Ba2Y3(MoO4)8 crystals. An Yb3+:Li3Ba2Y3(MoO4)8 crystal with dimensions of 25 mm × 11 mm × 15 mm has been successfully grown by the TSSG method. The spectral parameters of Yb3+:Li3Ba2Y3(MoO4)8 crystal have been estimated. The laser performance parameters β min, I sat, and I min of the crystal have been also established. The results regard the Yb3+:Li3Ba2Y3(MoO4)8 crystal as a potential solid-state laser crystal material.
Keywords: Crystal growth; Photoelectron spectroscopic;

Ce modification of commercial AZ alloys has great potential for the development of Mg alloys with improved formability and creep resistance. Because the solid solubility of Ce in (Mg) solid solution is extremely low, the precipitation of Ce containing intermetallics is expected even at low Ce concentrations. The Ce–Mg–Zn phase diagram at 350 °C was studied in this work by means of diffusion couple techniques. Precipitation of intermetallic phases in the Mg-rich corner has been analyzed using Scanning electron microscopy (SEM) and their compositions were determined by energy dispersive spectroscopy (EDS).
Keywords: Metals and alloys; Phase diagrams; Diffusion; Scanning electron microscopy (SEM);

Magnetic properties of the PrCo4 −  x Ni x B borides by H. Ağıl; N. Kervan; S. Kervan; H. Sözeri; A. Gencer (437-440).
In this work, the crystal structure and the magnetic properties of the PrCo4 −  x Ni x B compounds for 0 ≤  x  ≤ 4 have been studied by X-ray powder diffraction (XRPD), magnetization and differential scanning calorimetry (DSC) measurements. These compounds crystallize in a hexagonal CeCo4B-type structure with P6/mmm space group. The substitution of Ni for Co leads to a decrease of the unit-cell parameters a and the unit-cell volume V, while the unit-cell parameter c increases. The magnetic measurements indicate that the samples with x  ≤ 2 are ordered magnetically. The samples with x  = 3 and x  = 4 are paramagnetic. The Curie temperature and the saturation magnetization decrease with increasing Ni content x.
Keywords: Magnetic materials; Magnetic properties; X-ray diffraction; Differential scanning calorimetry (DSC);

Crystallization of Zr60Fe20Cu20 amorphous alloy by S. Michalik; K. Saksl; P. Sovák; K. Csach; J.Z. Jiang (441-446).
Amorphous structure and phase transformations of the rapidly solidified Zr60Fe20Cu20 alloy have been investigated by the DSC, in-situ high temperature XRD and EXAFS techniques. The performed experiments on the amorphous alloy proved significantly shorter Zr–Fe and Zr–Cu distances than those expected from the hard sphere atom model, corroborating strong bonding between Zr and transition elements. The crystallization of Zr60Cu20Fe20 amorphous alloy underwent three-stage process. The formation of stable cubic Zr(Cu, Fe) and tetragonal Zr2(Cu, Fe) phases was confirmed and the formation of a quasicrystalline phase was suggested.
Keywords: Metallic glasses; Quasicrystals; X-ray diffraction;

Characterization of some lead vanadate glasses by Yasser B. Saddeek; Essam R. Shaaban; Kamal. A. Aly; I.M. Sayed (447-452).
Studies on lead vanadate glasses modified with Li2O have been carried out. Elastic properties and Debye temperature have been investigated using sound velocity measurements at 4 MHz. The ultrasonic and the IR spectroscopic studies have been employed to investigate the structure of lead vanadate glasses in the presence of Li2O. IR analysis indicates that increasing the vanadate content causes a shift of the bands to higher wave number and to higher relative area which was attributed to the higher dissociation energy of V2O5 than that of PbO. Thus, the average force constant of VO5 structural units increases with increasing V2O5 content. The change of density and molar volume with V2O5 content reveals that the decrease in density is related to the replacement of high dense PbO with low dense one V2O5, where the increase in the molar volume can be attributed to the larger packing factor of V2O5 than that of PbO. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of V2O5 on the coordination number of the vanadate and lead structural units.
Keywords: Vanadate glasses; IR; Density; Elastic properties;

Tantalum oxide films were synthesized by pulsed laser deposition (PLD). The influences of annealing temperatures and oxygen pressures on the crystalline, morphological and optical properties were investigated. Experimental results indicate that annealed film became crystallized in orthorhombic structure at 700 °C. The root-mean-square (RMS) roughness of the film became higher with the increase of annealing temperature. The transmittance and the optical band gap of the film increased with the increase of annealing temperature and the increase of annealing oxygen pressure. In addition and interestingly, crystallinity led to a decrease of transparency due to the increase of scattering losses, which resulted from the polycrystalline structure and the increase of RMS roughness. At the optimized ambience of 600 °C and 20 Pa, the transmittance of the annealed film achieved about 93% (the transmittance of bare substrate) at its peak values. And its optical band gap was 4.18 eV, which was close to the theoretical value of 4.2 eV.
Keywords: Tantalum oxide films; Post-annealing; Crystal structure; Optical properties;

In this study, the influence of a wide range of reinforcements (SnO2, Cu, Y2O3, ZrO2  + 8 mol.% Y2O3 and TiB2) on the electrical resistivity of Sn–3.5Ag and Sn–3.5Ag–0.7Cu solders was investigated. The electrical resistivity test was conducted on the bulk samples of composite solders at ambient temperature. Results revealed that electrical resistivities of composites containing nanometer length scale reinforcement is not compromised for the optimal amount of reinforcement required to realize best tensile properties. This behavior was not displayed by composite containing micron size particles. The results of this study are expected to pave the way to develop lead-free nanocomposites especially for the industry using solid-state bonding technique.
Keywords: Lead-free solder; Nanocomposite; Electrical resistivity; Mechanical properties;

The paper aimed at the water vapour induced corrosion of the Fe–40 at.% Al alloy under applied constant loads using tensile apparatus. To interpret the registered experimental curves they were converted in accordance with Ternes method. Microfractographic investigations were conducted on specimens after cracking. Results reveal susceptibility of the iron aluminide to stress corrosion, and influence of heat treatment on this process.
Keywords: Intermetallics (based on FeAl); SEM; Stress corrosion;

Transformation of MgB2 powder into superconducting film via electrophoretic deposition technique by M.B. Kadam; B.B. Sinha; R.S. Kalubarme; S.H. Pawar (467-473).
Electrophoretic deposition of the commercially available MgB2 powder on stainless steel substrates from methanol dispersion medium is reported for the first time. Various deposition parameters such as deposition medium, quantity of powder loading, deposition potential and the time of deposition have been optimized. Films were subjected to heat treatment in flowing argon ambience and excess magnesium powder. Structural, morphological and FTIR studies of the films were carried out. The films are found to be adherent, uniform and with no traces of MgO. Films showed the superconducting transition in the range 38.5–39 K.
Keywords: Superconductors; Thermal analysis; Electrochemical reactions; Electrophoretic deposition; MgB2; Dispersion medium; A.C. magnetic susceptibility;

A comparative study of Si–C–N films on different substrates grown by RF magnetron sputtering by A.S. Bhattacharyya; S.K. Mishra; S. Mukherjee; G.C. Das (474-478).
Si–C–N nanocomposite thin films were deposited on industrially important substrates like silicon (1 0 0), borosilicate glass, and stainless steel (304SS) by radio frequency (RF) magnetron sputtering. The microstructural characterization was carried out by transmission electron microscopy (TEM) showing localized β-C3N4 in amorphous Si–C–N matrix, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The thermal mismatch occurring between the substrate and the coating resulted in variation in deposition rate, roughness and other mechanical properties like hardness and adhesion for the three different substrates. Both microindentation and nanoindentation were performed to estimate the hardness of the coatings. Scratch tests were used for the adhesion studies.
Keywords: Si–C–N; RF sputtering; Substrate effect;

We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K-edge and dc magnetic measurements performed on (La1−x Ca x )(Mn1−y Cu y )O3 samples (x  = 0.37 and 0.75 and y  = 0.03 or 0.08), thus comparing the effects determined by the partial Mn substitution with Jahn–Teller Cu2+ ions with those induced by the already studied analogous substitution of Mn with non-Jahn-Teller Cr3+.Hence, in the present paper we complete our study on the influence of chemical Mn site substitutions on the nanoscale phase inhomogeneity characteristic of these strongly correlated electron systems.We observe that the Cu2+ substitution determines two very different effects in the two compositions belonging from the opposite sides of the phase diagram. In the x  = 0.37 case it weakens the ferromagnetic ordering thus favouring the antiferromagnetic charge ordered phase component, while in the x  = 0.75 one it does not significantly modify the charge ordering already present in the system, differently from what previously observed in presence of non-Jahn-Teller Cr3+ substitution.
Keywords: Oxide materials; Phase transitions; Magnetic measurements; EXAFS;

This paper reports the growth, structure and optical characterization of a new laser crystals Nd3+:Li3Ba2Gd3(WO4)8. Li3Ba2Gd3(WO4)8 compound crystallizes in the monoclinic system with space group C2/c, and cell unit parameters: a  = 5.217(3) Å, b  = 12.763(9) Å, c  = 19.204(13) Å, β  = 91.928(17)° and Z  = 2. Nd3+:Li3Ba2Gd3(WO4)8 crystals have been grown by TSSG method. The spectroscopic characterization of Nd3+:Li3Ba2Gd3(WO4)8 crystals was investigated. In comparison with the other Nd3+-doped tungstate crystals, Nd3+:Li3Ba2Gd3(WO4)8 crystal has broad absorption band, large absorption cross-section and value of σ em τ. The results regard Nd3+:Li3Ba2Gd3(WO4)8 crystal as a potential solid-state laser material for diode laser pumping.
Keywords: Crystal growth; Crystal structure and symmetry; Photoelectron spectroscopic;

Optical properties and formation mechanism of radial ZnO hexagonal nanoprism clusters by Deng Yuan; Guang-Sheng Wang; Yan Xiang; Yang Chen; Xuan-Qiao Gao; Guo Lin (489-492).
Radial ZnO clusters have been synthesized in a large-scale by a simple microemulsion method using sulfonate-polystyrene (S-PS) as a template. The clusters are formed by the radial growth of ZnO hexagonal nanorods. The product is characterized by using XRD, SEM, TEM, FT-IR, and photoluminescence spectra (PL). Furthermore, the SEM images indicate that the radial ZnO structures possess hexagonal prisms structures. On the meanwhile, FT-IR spectrum reveals that S-PS is present in the radial ZnO nanostructures, and the PL spectrum shows a sharp UV emission. As a result, the formation mechanism of the radial ZnO nanostructures has been proposed.
Keywords: Nanostructure; Low dimensional structures; Zinc compound;

Nanocrystalline LaMnO3 powders were synthesized by sol–gel combustion method. The effect of citric acid (CA) to metal nitrates (MN) molar ratio of the precursor solution on the structure of gels and as-synthesized powders, combustion behavior, and microstructure of as-synthesized powders was investigated with the help of thermal analysis, infrared spectra, X-ray diffraction technique and scanning electron microscopy. The results show that the structure of gels and as-synthesized powders is influenced significantly by the molar ratio of citric acid to metal nitrates. The combustion rate decreases with increasing the CA/MN molar ratio. The crystallite size of the as-formed LaMnO3 powders increases with increasing the CA/MN molar ratio. The crystalline phases transform from cubic phase to orthorhombic phase with increasing the CA/MN molar ratio from 0.5 to 1.5.
Keywords: Nanocrystalline LaMnO3; Sol–gel combustion synthesis; Phase transitions;

Synthesis of ZnTa2O6 nano-powders by citrate sol–gel method by YingChun Zhang; BaoJian Fu; Xiu Wang (498-500).
The ZnTa2O6 nano-powders have been synthesized using Ta2O5 as starting materials at a low temperature by sol–gel method in this study. The decomposition of precursors, crystal structure and microstructure of ZnTa2O6 powders were characterized by differential thermal analysis (DTA)/thermogravimetry (TG), X-ray diffraction (XRD) and SEM techniques. The effects of pH values on the crystal structure and microstructure of ZnTa2O6 nano-powders were also investigated. XRD and TG/DTA results show that the single phase of ZnTa2O6 for synthesized powder can be obtained by calcining the precursor at 900 °C. The average particle size of ZnTa2O6 ranges from 30 nm to 96 nm with varying the pH values.
Keywords: Ceramic; Sol–gel processes; Nanostructures; X-ray diffraction;

Hydrogen-storage properties of melt spun Mg–23.5 wt%Ni milled with nano Nb2O5 by MyoungYoup Song; SungNam Kwon; Jong-Soo Bae; Seong-Hyeon Hong (501-506).
Melt spun Mg–23.5Ni and 90%(ms Mg–23.5Ni)–10%Nb2O5 alloys were prepared by reactive mechanical grinding. The activated 90%(ms Mg–23.5Ni)–10%Nb2O5 alloy has higher hydriding and dehydriding rates than the activated melt spun Mg–23.5Ni alloy. The activated 90%(ms Mg–23.5Ni)–10%Nb2O5 alloy absorbs 4.70 wt% H for 10 min at 573 K under 12 bar H2, and desorbs 4.75 wt% H for 25 min at 573 K under 1.0 bar H2. The added Nb2O5 and/or their pulverization during mechanical grinding are considered to make Mg particles finer. This is considered to make the activated 90%(ms Mg–23.5Ni)–10%Nb2O5 alloy has higher hydriding and dehydriding rates than the activated melt spun Mg–23.5Ni alloy. The hydrogen-storage properties of the 90%(ms Mg–23.5Ni)–10%Nb2O5 alloy were compared with those of other alloys prepared under similar conditions.
Keywords: Metal hydrides; Rapid-solidification; Quenching; Kinetics; X-ray diffraction;

Microstructure and optical properties of N-incorporated polycrystalline ZnO films by X.C. Wang; W.B. Mi; S. Dong; X.M. Chen; B.H. Yang (507-512).
N-incorporated ZnO films were fabricated using rf magnetron sputtering under different nitrogen flow rates (P N). The surface roughness and ZnO grain size are dependent on P N. Meanwhile, Zn nitride appears in the films as P N increases. N incorporation affects the intensity of the diffraction peaks from the different lattice planes. At P N  = 20%, the film grows with ZnO (0 0 2) lattice. The incorporated N exists in the forms of Zn nitride and atomic N. The optical band gap (E g) of the N-incorporated ZnO films decreases from 3.17 to 2.95 eV linearly with the increase of P N. The photoluminescence peaks in the region of 2.4–2.7 eV come from the transition between conduction band edge and oxide antisite defects (OZn), and also be influenced by oxygen vacancies (Vo).
Keywords: Thin films; Semiconductors; X-ray diffraction; Crystal structure and symmetry;

The controllable synthesis of hexagonal flower-like Zn-doped CdSe (Cd1−x Zn x Se, x  = 0.1) microstructures from the solid air-stable precursor has been achieved by two facile steps: first, precursors were prepared directly through precipitation reactions of stoichiometric cadmium acetate, zinc acetate and sodium selenite in distilled water under ambient condition; second, pure hexagonal phase flower-like Cd0.9Zn0.1Se were produced via solvothermal treatment of the precursor compound in ethylenediamine (en) at 180 °C. The products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrum (EDS) and UV–vis absorption spectroscopy. It was observed that the optical band gap energies of the as-synthesized flower-like Cd0.9Zn0.1Se microstructures shift toward shorter wavelengths compared with CdSe.
Keywords: Nanostructured materials; Chemical synthesis; Crystal growth; X-ray diffraction;

The modified PMnN-PZT based piezoelectric ceramics of composition Pb0.99Ca0.01 [(Mn1/3Nb2/3)x  − (1 −  x)(Zr y Ti1 y )]O3 (0.02 ≦  x  ≦ 0.07, 0.47 ≦  y  ≦ 0.54) were synthesized by B-site oxide precursor method (BO method) and conventional mixed oxide method (MO method). The morphotropic phase boundary (MPB) was adjusted by varying the Zr ratio to compromise the balance between the piezoelectric properties and the temperature stability of static capacitance. The influence of PMnN content on the microstructure, electrical, temperature stability and mechanical properties of the samples synthesized using these two methods were investigated and compared. Results showed that the samples synthesized using the BO method not only lowered the sintering temperature (from 1260 °C to 1150 °C) without adding any sintering aids but also exhibited piezoelectric properties, temperature stability of resonance frequency (TCF) and elastic stiffness coefficient superior to those of MO-type piezoelectric ceramics. Experimental results showed that the bulk density (g/cm3), dielectric loss, K t , K p , d 33, Q m , c 33 D (×1010  N/m2), and TCF (ppm/°C) of BO-type ceramics were 7.78, 0.0022, 0.5, 0.63, 345, 1450, 14.65, and 85 compared to those of MO-type ceramics (i.e., corresponding values of 7.65, 0.0025, 0.48, 0.58, 280, 1400, 14.54, and 105) with optimum composition of x  = 0.04. The obvious improvement is due to the fine-grain microstructure and chemical homogeneity. In addition, two types of narrow-band therapeutic transducers were fabricated and compared. According to the experimental results, the PMnN-PZT based piezoelectric ceramics using the BO method are found to be suitable for in ultrasonic therapeutic transducer applications.
Keywords: Piezoelectric properties; Morphotropic phase boundary; Temperature stability; PMnN-PZT; Therapeutic transducer;

The morphology and growth kinetics of intermetallic compounds that are formed in the interface of H13 tool steel and A380 molten aluminum has been investigated through immersion experiments. The effect of addition of micro alloying elements to the melt on the formation and thickness of intermetallic layer was also studied. Microstructural investigation showed that three intermetallic layers formed through the liquid–solid reaction during immersion of steel samples in the liquid aluminum at a temperature of 680 °C for the duration time of 2 min to 2.5 h. These intermetallic compounds are Al8Fe2Si, Al5FeSi and Al12Fe5Si. The effect of nitride coating of the surface of H13 steel on the growth of intermetallic phases has also been studied. Micro alloying elements such as strontium and titanium have been used in the melt and their effects on the morphology of intermetallic compound and their growth rate have been investigated by the immersion experiments at the temperature of 680 °C for the time of 0.5–2.5 h. The results showed that two layers of Al8Fe2Si and Al5FeSi formed at the interface and Al12Fe5Si layer was not observed. Nitride coating decreased the overall thickness of the intermetallic layer about 50% after immersion time of 0.5 h. Addition of micro alloying elements such as Sr (0.05 wt%) and Ti (0.2 wt%) to the melt decreased the total thickness of the intermetallic layer about 31% after immersion of steel for 0.5 h in the melt. Both nitride coating and addition of strontium (0.05 wt%) and titanium (0.2 wt%) micro alloying elements to the melt had the most influence on decreasing the overall thickness of the intermetallic layer. The thickness of the intermetallic layer decreased about 60% after immersion of steel for 2.5 h in the aluminum melt. The experimental results clearly indicate the beneficial effect of strontium on the kinetics of the formation and growth of the intermetallic layers.
Keywords: Intermetallics; Surfaces and interfaces; Scanning electron microscopy; Micro alloying elements; Growth kinetics;

The structural and electronic properties of BN and BP compounds and BN x P1−x alloys have been investigated by full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The total energies and electronic band structures of these compounds have been calculated for different approximations of exchange–correlation energy. The comparative study has showed that the Perdew–Wang-generalized gradient approximation (PW-GGA) is the best one to produce the measured structural quantities of the compounds, such as the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. The electronic quantities of the compounds, such as the width of the valance band and energy gaps at high symmetry points have been found to be in good agreement with the corresponding measured ones when the compounds were defined by the lattice constants of PW-GGA scheme. The PW-GGA approach was also applied on BN x P1−x alloys for obtaining the variation of the equilibrium lattice constants, bulk moduli, and minimum energy gaps as a function of the nitrogen concentration within the range of 0 < x < 1 . It is found that these variations having large bowing parameters exclude the Vegard’s linear rule.
Keywords: BN; BP; BN x P1−x ; DFT; FP-LAPW; PW-GGA; Structural properties; Electronic properties;

Molecule-based electrorheological material, a β-cyclodextrin derivative and its rare earth complexes by Yun-Ling Jia; Li Huo; Yun Ma; Jun-Ran Li; Shao-Hua Zhang; Ming-Xiu Li (538-543).
Molecule-based electrorheological (ER) materials as a novel type of ER materials, dicarboxylic acid [H2(β-CD-A)] of β-cyclodextrin (β-CD) and the rare earth (RE) complexes [(β-CD-A)3(RE)2] (RE = Y, La, Gd) materials, were synthesized, the ER performance and dielectric property of the materials were studied. Our results show that these molecule-based ER materials exhibit clear ER effect. The ER performance of β-CD can be enhanced with the formation of H2(β-CD-A) and RE complexes. The ER activity of the yttrium complex is the highest among these RE complexes. The dielectric property plays an important role in influencing the ER property of these materials.
Keywords: Electrorheological material; Chemical synthesis; Electrorheological property;

In the present investigation sol–gel-based ZrO2 ceramic film was obtained using zirconium acetate as the precursor material. The film was deposited on AZ91D magnesium alloy by a dip-coating technique. An uniform stannate conversion coating as chemical pretreatment was employed as an intermediate layer prior to deposition of the ZrO2 film in order to provide advantage for the formation of sol–gel-based ZrO2 layer. The corrosion properties, structure, composition and morphology of these coatings on AZ91D magnesium alloy were studied by potentiodynamic polarization tests, EIS, XRD, SEM, respectively. According to the electrochemical tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this new environment-friendly surface treatment.
Keywords: Magnesium alloy; Sol–gel processes; Thin films; Corrosion; Electrochemical impedance spectroscopy;

The self-assembly of solid or tubular ZnO microrods into hexagonal twinning microprisms were achieved by choosing different solvents under a simple hydrothermal route. The composed solid or tubular ZnO microrods, as self-assembly building blocks, are single crystals with the [0 0 0 1] growth crystallographic direction; and most of them have diameters of ∼2.8 μm, lengths of up to ∼4.6 μm. Room-temperature photoluminescence spectrum of the solid ZnO microstructures reveals a strong emission band located at 397 nm and two broad emission bands at about 485 nm, 528 nm, respectively. A possible growth mechanism has been proposed. It is expected that the present ZnO microstructures have some potential applications in optoelectronic devices.
Keywords: Semiconductors; Crystal growth; Crystal structure and symmetry; Scanning and transmission electron microscopy; Anisotropy;

The microwave dielectric properties and the microstructures of the (1 −  x)Mg4Nb2O9xSrTiO3 ceramic system prepared by the conventional solid-state route were investigated. SrTiO3 was employed as a τ f compensator and was added to Mg4Nb2O9 to achieve a temperature-stable material. Corundum-structured Mg4Nb2O9 and perovskite-structured SrTiO3 were coexisted and the two-phase system was confirmed by the XRD and EDX analysis. Dielectric properties are correlated to the sintering temperature and the compositional ratio of the specimens. Although the ɛ r of the specimen could be boosted by increasing amount of SrTiO3, it would instead render a decrease in the Q  ×  f. The τ f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, τ f could be adjusted to near-zero by mixing 60 mole% Mg4Nb2O9 and 40 mole% SrTiO3. A dielectric constant (ɛ r ) of 21.02, a high Q  ×  f value of 112,000 GHz (measured at 9.7 GHz) and a temperature coefficient of resonant frequency (τ f ) of 1.6 ppm/°C were obtained for 0.6Mg4Nb2O9–0.4SrTiO3 sintered at 1300 °C for 4 h. It is proposed as a very promising dielectric material for low-loss microwave and millimeter wave applications.
Keywords: Crystal growth; Dielectric response;

In recent years, the consumption of metal matrix composites (MMCs) materials in many engineering fields has increased enormously. Most industries are usually looking for replacement of ferrous components with lighter and high strength alloys like Al metal matrix composites. Despite the superior mechanical and thermal properties of particulate metal matrix composites (PMMCs), their poor machinability is the main drawback to their substitution to other metallic parts. Machining is a material removal process which is important for many stages prior to the application or assembling of the components. Accordingly, the need for accurate machining of composites has also increased tremendously. This study addresses the modeling of the machinability of self-lubricated aluminum/alumina/graphite hybrid composites synthesized by powder metallurgy (P/M). In the present work, a feed forward back propagation artificial neural network (ANN) system is used to investigate the influence of some parameters on the thrust force and cutting torque in the drilling processes. Experimental data collected were tested with artificial neural network technique. Multilayer perceptron model has been constructed with feed forward back propagation algorithm using the input parameters of cutting speed, cutting feed, and volume fraction of the reinforced particles. Output parameters were the thrust force and cutting torque. On completion of the experimental test, an ANN is used to validate the results obtained and also to predict the behavior of the system under any condition within its operating range. The predicted thrust force and cutting torque based on the ANN model were found to be in a very good agreement with the unexposed experimental data set. The modeling results confirm the feasibility of the ANN and its good correlation with the experimental results. The degrees of accuracy of the prediction were 93.24% and 94.17% for thrust force and cutting torque, respectively. It is concluded that ANN is an excellent analytical tool, which can be used for other machining processes, if it is well trained.
Keywords: Powder metallurgy; Metal matrix composites; Drilling; Machinability; Artificial neural network; Modeling;

Near room temperature magneto caloric effect in V doped La0.67Ca0.33MnO3 ceramics by P. Nisha; P.N. Santhosh; K.G. Suresh; C. Pavithran; Manoj Raama Varma (566-571).
La0.67Ca0.33MnO3 doped with different amounts of V, resulting in the series La0.67Ca0.33Mn1−x V x O3 [x  = 0.03, 0.06, 0.1, 0.15, 0.25, 0.5] was synthesized by conventional solid-state ceramics route. Heat treatment conditions during synthesis were optimized to have small changes in the Curie temperature (T C ). The compounds with x  > 0.06 were found to have the additional LaVO4 phase. A quantitative analysis of the extra phase with increase in V doping was investigated by the Rietveld refinement of the X-ray diffraction patterns. Variation of magnetic and magnetocaloric properties at different temperatures and magnetic fields was studied. Magnetocaloric effect has been studied in terms of isothermal magnetic entropy change (ΔS M ). Magnetization was found to change drastically at around 275 K and the isothermal magnetic entropy change was found to peak in the temperature range 265–275 K. With increase in V content, ΔS M initially shows a considerable increase and then a decrease at higher V concentrations.
Keywords: Magnetic measurements; X-ray diffraction; Magnetically ordered materials:crystal structure and symmetry;

HfB2–SiC and HfB2–HfC–SiC dense composites have been prepared by self-propagating high-temperature synthesis (SHS) followed by spark plasma sintering (SPS) without the addition of any sintering aid.Starting from Hf, B4C, Si, and, when synthesizing the ternary system, also graphite powders, it was found that the SHS technique leads to the complete conversion of reactants to the desired products and the SPS allows for the full consolidation under the following optimal operating conditions: maximum dwell temperature (1800 °C), total processing time (30 min) and applied pressure (20 MPa). The obtained ternary composite displayed relatively low resistance to oxidation while the binary product exhibited low and thermally stable oxidation rate up to 1450 °C. In addition, the mechanical properties of both products are comparable to, and, in some cases better than, those related to analogous HfB2-based composites prepared with other processing routes. Moreover, the required consolidation conditions (processing time, temperature, and pressure) resulted to be milder in this investigation.
Keywords: Composites; Borides; Self-propagating high-temperature synthesis; Spark plasma sintering;

Effect of temperature on microstructures and properties of aluminized coating on pure magnesium by Fencheng Liu; Xianrong Li; Wei Liang; Xingguo Zhao; Yan Zhang (579-585).
Surface aluminizing on pure magnesium was conducted by diffusion aluminizing treatment in vacuum at 673 K, 693 K and 718 K. The microstructures and phase constituents of the aluminized coating were investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy disperse spectrometry (EDS). The results revealed that an Al-rich coating had been formed on the surface of magnesium specimens by the solidification of the liquid layer formed between the magnesium substrate and the aluminum particles. The microstructure of the aluminized coating was typical hypoeutectic structure, which contained a large amount of intermetallic compound, such as β-Mg17Al12. The composition profiles and microstructures of the aluminized coating were depended on the heating temperature. The results of micro-hardness tests indicated that the micro-hardness value of the specimen's surface increased due to the formation of the intermetallic compound. The results of immersion corrosion tests and electrochemical corrosion tests in 5 wt.% NaCl solution showed that the corrosion resistance of the coated specimens had been increased significantly, for example, the open circuit potential changed from −1.250 V (vs. SCE) to −0.866 V (vs. SCE) and the corrosion current density decreased from 1.3 × 10−3  mA/cm2 to 1.0 × 10−4  mA/cm2.
Keywords: Surfaces; Heat treatment; Vacuum; Corrosion;

Mixed-phase TiO2 nanoparticles preparation using sol–gel method by S. Mahshid; M. Askari; M. Sasani Ghamsari; N. Afshar; S. Lahuti (586-589).
Biphase TiO2 nanoparticles have been prepared by sol–gel method. Water/titanium molar ratio (r) has been used to control the hydrolysis and condensation of titanium isopropoxide in solution producing titanium oxide with two different polymorphs. The influence of crystallite size and morphology of prepared TiO2 on the phase transformation of the resultant materials has been investigated. Synthesized powders were characterized by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Different trends can be observed in the phase transformation and particle growth of the prepared titanium oxide nanomaterial. It was concluded that, the rate of particle growth and the final particle size as well as phase transformation were a function of molar ratios (r). The percentage of rutile in the final material was 23%.
Keywords: TiO2 Nanostructures; Sol–gel chemistry; Phase transactions;

Stable, easily sintered BaCe0.5Zr0.3Y0.16Zn0.04O3−δ electrolyte-based proton-conducting solid oxide fuel cells by gel-casting and suspension spray by Bin Lin; Yingchao Dong; Songlin Wang; Daru Fang; Hanping Ding; Xiaozhen Zhang; Xingqin Liu; Guangyao Meng (590-593).
Protonic ceramic membrane fuel cells (PCMFCs) based on oxide proton conductors exhibit more advantages than traditional solid oxide fuel cells (SOFCs) based on oxygen-ion conducting electrolytes, such as low activation energy and high energy efficiency. In order to develop a simple and cost-effective route to fabricate PCMFCs with SrCo0.9Sb0.1O3−δ (SCS) cubic perovskite cathode, a dense BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (BCZYZn) electrolyte was fabricated in situ metal oxide on a porous anode support by gel-casting and suspension spray, which is cost-effective, easy to realize, and suitable for mass-production. The key part of this process is to directly spray well-mixed suspension of BaCO3, CeO2, ZrO2, Y2O3 and ZnO instead of pre-synthesized BCZYZn ceramic powder on the anode substrate. With SCS cubic perovskite cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H2 as fuel and the static air as oxidant. An open-circuit potential of 0.987 V, a maximum power density of 364 mW cm−2, and a low polarization resistance of the electrodes of 0.07 Ω cm2 was achieved at 700 °C.
Keywords: Electrode materials; Thin films; Chemical synthesis; X-ray diffraction; Ionic conduction;

Interconnected flacks and nano-worms structures of cobalt oxide on glass and copper substrates have been deposited using chemical bath deposition method from aqueous alkaline cobalt chloride (CoCl2·6H2O) solution. The cobalt oxide films were examined with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical absorption and electrical resistivity techniques. The structural analyses showed that as-deposited amorphous CoO(OH) films converted into crystalline Spinel Co3O4 after annealing. Nanocrystalline grains with some overgrown clusters of cobalt oxide were revealed from surface morphological studies. TEM study showed the formation of nanocrystals with a diameter ranging from 5 to 10 nm. From optical studies, band gap of 2.4 eV was estimated for cobalt oxide thin film. The electrical resistivity exhibited semiconducting behavior of cobalt oxide thin film.
Keywords: Cobalt oxide; Thin films; Chemical deposition; Nanostructure;

Effect of cobalt substitution on structural, magnetic and electric properties of nickel ferrite by R.C. Kambale; P.A. Shaikh; S.S. Kamble; Y.D. Kolekar (599-603).
A series of cobalt-doped nickel ferrite with composition of Ni(1−x)Co x Fe2O4 with x ranges from 0.0 to 0.8 (in steps of 0.2) was prepared by using standard ceramic technique. The confirmation of single-phase formation and structural analysis were carried out by employing X-ray diffraction technique. The electrical DC resistivity measurement was done by using usual two probe method in the temperature range from room temperature to 600 °C. Room temperature resistivity measurements show the decrease in resistivity with increase of cobalt concentration. The studies on resistivity as a function of temperature shows that all the sample obeys the semiconducting behavior. B–H hysteresis measurement was carried out at room temperature under the field of 2.4 kOe and this measurement with the increase of Co2+concentration yields the monotonic increase of saturation magnetization (M s) and decrease in coercive field (H c) at higher Co2+concentration (x  > 0.4). Ferrites with such behavior are important for magnetic recording media. In view of this, we have studied the various properties of Co-doped Ni ferrite.
Keywords: Magnetically ordered materials; Powder metallurgy; X-ray diffraction; Electronic transport; Magnetic measurements;

A Na3V2(PO4)2F3 cathode material for lithium ion batteries was prepared by using a sol–gel method to prepare precursor, and then heat treated the precursor at 650 °C based on TG analysis. Transmission electron microscopy showed that the material had a small particle size about 20 nm. The Na3V2(PO4)2F3 particles were embedded in a network of residual carbon. The content of residual carbon was determined to be 8.5 wt.%. This residual carbon enhanced the electronic conductivity of the material, which was measured to be 1.0 × 10−3  S cm−1. The electrochemical insertion mechanism of Na3V2(PO4)2F3 gradually shifted from a predominant Na+ insertion to a Li+ insertion in the initial 10 cycles. The material showed a reversible discharge capacity of 117 mAh g−1, with quite good capacity retention. The good electrochemical performance of Na3V2(PO4)2F3 was attributed to its NASICON-type structure, which provided a large ion diffusion coefficient about 7.2 × 10−10  cm2  s−1. The good electrochemical performance of Na3V2(PO4)2F3 provides an example to use sodium-based materials directly as cathode materials for lithium ion batteries.
Keywords: Lithium ion battery; Cathode material; Na3V2(PO4)2F3; Sol–gel method; Electrochemical property;

Effect of Al2O3/YSZ microstructures on wear and mechanical properties of cutting inserts by Ahmad Zahirani Ahmad Azhar; M.M. Ratnam; Zainal Arifin Ahmad (608-614).
Wear and mechanical properties of ceramic cutting inserts produced from Al2O3/yttria stabilized zirconia (YSZ) system has been investigated. The YSZ compositions were varied from 0 wt% to 100 wt%. Each Al2O3 and YSZ composition was mixed, uniaxially pressed into rhombic 80° cutting inserts and sintered at 1600 °C for 4 h in pressureless condition. Study on the effect of the microstructure of the inserts on the mechanical and physical properties such as nose wear, Vickers hardness and fracture toughness has been carried out. Mild steel (AISI 1018) was used as the workpiece in the machining tests using the cutting inserts. The results show that 20 wt% of YSZ produced the minimum wear area. When the amount of YSZ was increased from 20 wt% to 100 wt%, the wear area also increased from 0.039 mm2 to 0.182 mm2. However, the Vickers hardness of the inserts decreased with the increase of YSZ, while the fracture toughness of the cutting inserts shows a continuous increase up to 60 wt% YSZ. Above 60 wt% of YSZ, the microstructure of the polished samples started to show microcracks and formed larger grain sizes of YSZ, thus hindering the transformation toughening mechanism from functioning effectively.
Keywords: Cutting inserts; Wear; Microstructure; Microcracks;

The nanocomposite WC–MgO powders were prepared at room temperature by reactive milling of low-cost WO3, Mg and graphite powders under argon gas atmosphere in a planetary ball milling. Powder samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The milling energy was calculated using a collision model and the milling energy maps were attained. The effects of milling parameters (including milling speed, ball-to-powder weight ratio and milling time) on the formation mechanism have been illuminated by the obtained milling energy maps. Results show that WC–MgO can be formed via Self-propagation High-temperature Synthesis (SHS) when the effective extensive factor E b is above 38.24 kJ g−1  s−1, and it also can be formed from gradual reaction when E b is between 22.12 kJ g−1  s−1 and 38.24 kJ g−1  s−1. As the energy map demonstrates, the total energy E t required for fabricating WC–MgO through SHS ranges from 25.61 × 106  kJ g−1 to 61.82 × 106  kJ g−1, while more than 112.83 × 106  kJ g−1 is necessary for gradual reaction one. These milling energy maps are proposed as a tool for better understanding of the synthesis and formation of WC–MgO by high-energy reactive milling.
Keywords: WC–MgO; High-energy ball milling; Formation mechanism; Milling energy map;

Preparation and characterization of monodisperse Ag nanoparticles doped barium titanate ceramics by Fengtao Du; Pengfei Yu; Bin Cui; Haiou Cheng; Zhuguo Chang (620-623).
The phase, microstructure and dielectric properties of monodisperse Ag nanoparticles doped BaTiO3 ceramics with different contents of silver (0.0–20.0 mol%) were investigated in this paper. The XRD analysis showed that no phases other than BaTiO3 and silver were observed in the ceramics; it implied that silver did not react with BaTiO3 during sintering process. A small amount of monodisperse Ag nanoparticles (<0.5 mol%) was added to BaTiO3 ceramics could improve the sintered density; more content of monodisperse Ag nanoparticles (0.5–2.0 mol%) would decrease the relative density; larger content of monodisperse Ag nanoparticles (>2 mol%) could still improve the relative density. As the content of monodisperse Ag nanoparticles increased, the permittivity of ceramics increased continuously, while the dielectric loss decreased first and then increased. The ceramic doped with 1.0 mol% monodisperse Ag nanoparticles had the better dielectric properties.
Keywords: Monodisperse Ag nanoparticles; BaTiO3; Ceramics; Permittivity;

In the present work, a new mechanical alloying method, which combines ball milling and dielectric barrier discharge plasma (DBDP) together, has been reported. By treating pure metals, such as Al, Fe and W and synthesis WC with this method, an obvious synergism of ball milling and DBDP has been revealed, which is characterized by concurrent action of high temperature and stress on the powder in a very short time. Owing to the synergism of ball milling and DBDP, the fabricated metal powder has unique features, such as lump-like morphology with very fine primitive particles and high specific surface area. The chemical activity of the powders is very high, which makes possible the formation of nanostructured tungsten carbides at a temperature much lower than that in conventional carburizing of W. This provides a potential method for fabricating ultra fine powders and synthesizing metal ceramics.
Keywords: Mechanical alloying; Ball milling; Dielectric barrier discharge plasma;

In this paper, we report the influence of silver nanoparticles (NPs) on the luminescence properties of TeO2–ZnO–Nb2O5–MoO3 glass doped with trivalent praseodymium (Pr3+) ions. From the XRD, Raman and DTA measurements, glasses structural and thermal properties were determined. The experiments were performed with samples containing different concentrations of NPs controlled by heat-treatment of the glass. The enhancement of the Stokes luminescence with an increase of the NPs concentration was observed for these samples excited at 470 nm. The influence of the NPs on the frequency upconversion (anti-Stokes) emissions of Pr3+ under excitation at 586 nm was also investigated, in resonance with the 3H41D2 transition. The excited Pr3+ ions exchange energy in the presence of the nanoparticles, originating efficient conversion from orange to blue. The enhancement in the intensity of the luminescence at ∼493 nm, corresponding to the 3P03H4 transition, is due to the influence of the large local field on the Pr3+ ions, which are located near the metallic nanoparticles.
Keywords: Amorphous materials; Liquid quenching; Luminescence; Upconversion;

The effect of mechanical hard/soft matching of raw powder and substrate in the cold gas dynamic spraying process (CDSP) on the formation of intermetallic compounds was examined. Instead of pre-alloyed materials, pure Al and Ni were selected as a soft and a hard material, respectively, and post-annealing was used for compound formation. Most of the aluminide layers were observed in the coated layer, but not in the substrate, along with the entire original interface for both Al coating on a Ni substrate and vice versa. Thickening of the compound layer depended mainly on the creation of defects during spraying and intrinsic diffusivity of atoms moving toward the coating side. When Ni was coated, the compound layer was made thicker by fast diffusion of Al, while the thickness was limited in soft Al coating on hard Ni substrate. However, the composition of the compound can be affected by relative transfer of diffusing atoms toward both the coating and the substrate. So, for Ni coating on an Al substrate, most of the intermetallic compound formed was Ni-rich and conversion of the Al-rich compound was observed after post-annealing above 500 °C.
Keywords: Intermetallics; Surfaces and interfaces; Diffusion; Coatings;

The effect of nano-size MgO (40–60 nm) addition on both granular structure and volume thermal expansion measurements of polycrystalline (Cu0.25Tl0.75)-1234 was studied. The MgO-content x varied from 0.0 to 1.0 wt.% of the sample total mass. Granular investigation using scanning electron microscope revealed that both number and size of voids decreased as x increased from 0 wt.% to 0.6 wt.%. These results were supported by porosity calculation of the samples. The volume thermal expansion was calculated using X-ray powder diffraction from room temperature down to 80 K. The volume thermal expansion coefficient, at room temperature decreased, from 9.3 × 10−5  K−1 to 7.2 × 10−5  K−1 as MgO-concentration increased from 0.0 wt.% to 0.6 wt.% before it increased to 8.9 × 10−5  K−1 for MgO-concentration = 1 wt.%. The Debye temperatures, calculated from the volume thermal expansion coefficient measurements, were reported as a function of MgO-concentration and superconducting transition temperature.
Keywords: (Cu; Tl)-1234; Volume thermal expansion coefficient; MgO-nano particles; Debye temperature;

Effect of WO3 and MoO3 addition on LnTiTaO6 (Ln = Ce, Pr and Nd) microwave ceramics by H. Padma Kumar; M.K. Suresh; J.K. Thomas; Annamma John; Benny George; Sam Solomon (648-652).
The effect of dopants such as WO3 and MoO3 on the structural, processing and microwave dielectric properties of LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics is reported. Conventional solid-state ceramic route was used for the preparation of samples. The samples are calcined and sintered at optimized temperatures. A reduction of 50 °C in the sintering temperature was observed for all the samples. The crystal structure of the materials was analyzed using X-ray diffraction techniques and the surface morphology of the sintered samples was analyzed using scanning electron microscopy. The dielectric constant at microwave frequency range decreased on higher doping concentrations for all the samples but the quality factor is improved on small doping concentrations. The thermal stability of resonant frequency is also improved with doping on all the systems. A number of samples with improved microwave dielectric properties were obtained on all the systems and are suitable for practical applications.
Keywords: Ceramics; Rare earth alloys and compounds; Solid-state reaction; Sintering; Scanning electron microscopy, SEM;

In this study, first principles calculation results of the all elastic parameters, characteristic Debye temperatures, Poisson’s ratios, ultrasound velocities and full phonon dispersion spectra of two III–V group zincblende semiconductors, AlSb and GaSb, are presented. Calculations are based on plane wave basis sets together with Vanderbilt ultrasoft pseudopotentials in the framework of Density Functional Theory (DFT) with Perdew–Wang parameterization of generalized gradient approximation. The detailed total energy calculations are performed in order to obtain elastic stiffness coefficients using volume conserving (isochoric) strains on cubic zincblende phase. The phonon dispersion spectra are calculated in linear response approach. All calculated parameters as well as phonon dispersion spectra are in excellent agreement with experimental works and available theoretical calculations.
Keywords: Semiconductors; Elasticity; Phonons; Computer simulations;

The effect of WO3 additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO3–CaTiO3 ceramics system were investigated. The sintering temperature of WO3-doped 0.95MgTiO3–0.05CaTiO3 (95MCT) ceramics can be lowered to 1175 °C. The microwave dielectric properties are found strongly to correlate with the sintering temperature as well as the amount of WO3 addition. At 1250 °C 95MCT ceramics with 0.5 wt% WO3 addition gives a dielectric constant ɛ r of 20.3, a Q  ×  f value of 66,000 (GHz) and a τ f value of −8.2 ppm/°C. A band-pass filter is designed and simulated using the proposed dielectric to study its performance.
Keywords: Sintering; X-ray diffraction; Dielectric properties;

Synthesis and photoluminescence behavior of Bi4Ti3O12 powders obtained by the complex polymerization method by R.C. Oliveira; L.S. Cavalcante; J.C. Sczancoski; E.C. Aguiar; J.W.M. Espinosa; J.A. Varela; P.S. Pizani; E. Longo (661-670).
Bismuth titanate, Bi4Ti3O12(BiT) powders were synthesized by the complex polymerization method. The structural evolution as a function of heat treatment temperature of these powders was analyzed by X-ray diffraction (XRD) and micro-Raman (MR) spectroscopy. The optical properties were verified by ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) measurements. XRD patterns and MR spectra revealed that the BiT powders heat treated at 700  ° C for 2 h under oxygen flow crystallize in an orthorhombic structure without deleterious phases. UV–vis spectra indicated the presence of intermediary energy levels within the band gap of the powders heat treated at low temperatures. The maximum PL emissions of these materials were verified at around 598 nm, when excited by 488 nm wavelengths. Also, it was observed the presence of two broad PL bands, which were attributed to the intermediary energy levels arising from α -Bi2O3 and BiT phases.
Keywords: Clusters; Chemical synthesis; Optical properties; Luminescence;

Microstructural and electrical characteristics of reactively sputtered ZrN x thin films by Jian-Long Ruan; Ding-Fwu Lii; Horng-Hwa Lu; J.S. Chen; Jow-Lay Huang (671-675).
The effects of nitrogen flow rate on the microstructure, composition and electrical properties of ZrN x films prepared by reactive sputtering were investigated by X-ray diffraction, field-emission electron probe micro-analyzer, transmission electron microscopy, X-ray photoelectron spectroscopy and four-point probe method. Results indicated that the ZrN x films were crystallized in NaCl-type structure and showed a near-stoichiometric composition at nitrogen flow rate of 3 SCCM. The existence of residual oxygen in the ZrN x films was ascribed to the relatively high base pressure attained in the present work. The residual oxygen atoms in the ZrN x films may possibly substitute the nitrogen atoms or occupy the interstitial positions in the ZrN lattice, causing that the so-called near-stoichiometric films and the delay of occurrence for over-stoichiometric films in the N/Zr ratio evolution with nitrogen flow rate. The slightly larger lattice constant of ZrN x films compared with the ideal value of ZrN compound demonstrated the presence of residual oxygen atoms in the films. The electron scattering effects due to impurity atoms may be enhanced by the incorporation of residual oxygen atoms and were responsible for the overall raise in the resistivity of ZrN x films as a function of nitrogen flow rate, comparing with the value reported by previous studies.
Keywords: Thin films; Vapor deposition; Microstructure; Electrical properties;

Enhance upconversion photoluminescence intensity by doping Li+ in Ho3+ and Yb3+ codoped Y2O3 nanocrystals by Yunfeng Bai; Yuxiao Wang; Guanya Peng; Kun Yang; Xueru Zhang; Yinglin Song (676-678).
Infrared-to-visible upconversion emission spectrum is investigated in Li+, Ho3+ and Yb3+ codoped Y2O3 nanocrystals. By adding Li+ ion to the Y2O3:Ho3+/Yb3+ nanocrystal, the upconversion emission intensity is found being significantly enhanced comparing with that without Li+ ion. The two reasons for this enhancement are discussed: one is because of the modification of the local symmetry of the Ho3+ ion, and the other is because of the reducing number of OH groups. This indicates Li+ ion would be a wonderful photoluminescence intensifier for rare-earth.
Keywords: Y2O3:Ho3+; Yb3+; Li+; Nanocrystals; Upconversion; Enhance;

Microstructure and luminescence of surface-coated nano-BaMgAl10O17:Eu2+ blue phosphor by Z. Chen; Y.W. Yan; J.-M. Liu; Yi Yin; Hongmin Wen; Gaohua Liao; Chunlan Wu; Jiangqian Zao; Dehui Liu; Hongmin Tian; Chenshu Zhang; Shuidi Li (679-683).
MgF2 coating on BaMgAl10O17:Eu2+ (BAM) particles was obtained by an emulsion method. The chemical compositions, microstructure, and luminescent performance of surface-coating BAM were characterized by XRD, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), energy dispersion spectrum (EDS) and vacuum ultraviolet (VUV) excitation, respectively. The results indicate that a compact homogeneous MgF2 film is successfully coated on the surface of BAM particles by forming a chemical bond. Lengthening of fluorescence lifetimes were observed in surface-coated BAM phosphor attributed to less non-radiative rate due to coating. The luminescent performances of surface-coated BAM is improved due to the hanging-bonds and defects on the surface of nano-scale BAM particles being removed as well as non-radiative transition probability decreasing.
Keywords: Surface-coating; Emulsion method; BAM; Phosphor; Microstructure; Luminescent performance;

Synthesis and luminescent properties of CaMoO4:Tb3+, R+ (Li+, Na+, K+) by Xu Li; Zhiping Yang; Li Guan; Jianxin Guo; Ying Wang; Qinglin Guo (684-686).
A green-emitting phosphor CaMoO4 co-dopped by Tb3+ and alkali metals ions (R+) was fabricated by solid-state method. X-ray powder diffraction (XRD) analysis revealed that pure CaMoO4 was obtained. The excitation and emission spectra indicated that the phosphor could be well excited by ultraviolet light (375 nm) or blue light (488 nm) and emit green light at about 548 nm. The results showed that incorporation R+ (Li+, Na+ and K+) of into CaMoO4:Tb3+ phosphor could lead to a remarkable increase of photoluminescence or X-ray excited luminescence. It was found that the luminescent intensity depended on the doped concentration. The phosphor doped with 5 mol% Tb3+ and 5 mol% Na+ showed the highest luminescent intensity. The enhanced luminescence was regarded as the results of the creation of oxygen vacancies due to the Ca2+ sites occupied by charge compensator R+ ions.
Keywords: Phosphor; Luminescence; Tb3+; LED;

High temperature oxidation–reduction studies were undertaken on binary intermetallic compounds LnCu2 (Ln = La, Ce, Pr, Nd, Eu, Gd, Dy, Tm, Yb). A two steps cycle was optimized by O2-TG and H2-TG or H2-TPR studies along the lanthanide series. The oxidation mass uptake occurs over a wide range of temperature (200–900 °C), leading to two bimetallic copper–lanthanide oxides families according to the lanthanide: 3CuO·Ln2CuO4 (Ln = La, Pr, Nd, Eu, Gd) and 2CuO·Ln2Cu2O5 (Ln = Dy, Tm, Yb), except for CeCu2 that gives 2CuO·CeO2. Under hydrogen, all systems exhibit two reduction steps accompanied by mass losses in the 150–600 °C temperature range. The first mass loss is linked to the reduction of CuO, whereas the second mass loss corresponds to copper reduction in the Ln2CuO4 or Ln2Cu2O5 phase with concomitant formation of Ln2O3. The reduction products were characterized by XRD and different stoichiometries were obtained according to the lanthanide: 2Cu/CeO2, 3Cu/Ln2CuO4 or 2Cu/Ln2Cu2O5, after the first reduction step, and 4Cu/Ln2O3 after the second reduction one. Therefore, the binary intermetallic compounds LnCu2 decompose into a copper–rare earth oxide phase that after reduction leaves their surface highly enriched on the copper. The structure of the oxidized and reduced intermetallics can best be described as copper embedded in lanthanide oxides (Ln2O3) or “type supported catalysts” and exhibited activity for the 2-propanol oxidative dehydrogenation–dehydration reaction, which was also used to characterize their acid–base properties.
Keywords: LnCu2 intermetallic; Oxidation–reduction studies; 2-Propanol decomposition;

Carbon-coated copper–tin alloy anode material for lithium ion batteries by Sheng Liu; Qi Li; Yuxi Chen; Fengju Zhang (694-698).
Carbon-coated copper–tin alloy powders were prepared by heating of mixtures of thermoplastic poly(vinyl alcohol) and nano-sized copper–tin alloy particles in argon atmosphere. The products were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The electrochemical properties of the carbon-coated copper–tin alloy powders as anode materials for lithium batteries were studied by cyclic voltammetry (CV) and galvanostatic method. The anode showed high charge capacity up to 460 mAh g−1 and stable cyclic performance even after 40 cycles. This could be ascribed to the existence of inactive matrix Cu which buffered the large volume change in the course of Li–Sn alloying–dealloying process, and the presence of carbon layer of alloy particles which enhanced dimensional stability during Li–Sn alloying–dealloying electrochemical process.
Keywords: Copper–tin alloy; Carbon coating; Anode material; Lithium ion battery;

Formation of Ti3SiC2–Al2O3 in situ composites with Al2O3 content from 10 to 60 mol% was conducted by self-propagating high-temperature synthesis (SHS) involving the thermite reaction of Al with TiO2. The effect of the Al2O3 content formed was studied on combustion characteristics and the degree of product conversion. For the elemental powder compacts of Ti:Si:C = 3:1:2, the SHS processes are characterized by the high flame-front velocity ranging between 17.5 and 26.5 mm/s, high combustion wave temperature of 1450–1640 °C, and significant sample deformation caused by a solid–liquid reaction mechanism. The addition of the Al–TiO2 thermite mixture to the Ti–Si–C reaction system substantially reduced the flame propagation rate and reaction temperature, both of which decreased with increasing Al2O3 content in the synthesized composites. It was found that the reaction temperature was below the lowest eutectic point 1330 °C of the Ti–Si system when the composite with Al2O3 content higher than 40 mol% was produced. Due to the decrease of the Ti–Si eutectic and addition of the Al powder, the reaction mechanism of the 3Ti–Si–2C–Al–TiO2 system differs greatly from that of the 3Ti–Si–2C system. As a result, the reaction front velocities as low as 2–5 mm/s were observed in the cases of forming 20–60 mol% Al2O3-containing composites, which provides longer reaction time and then leads to an improvement in the product conversion. Based upon the XRD analysis, the formation of Ti3SiC2 and Al2O3 was confirmed and the presence of TiC and Ti5Si3 as the minor phases was also identified. The resulting Ti3SiC2 is typically elongated grains in a closely packed pattern and with a size of 10–30 μm in length and 1–3 μm in thickness. Moreover, the dispersion of Al2O3 grains about 1–2 μm in the composite is evident.
Keywords: Ceramics; Composite materials; Solid-state reactions; X-ray diffraction; SEM;

Processing of porous TiNi alloys using magnesium as space holder by Tarık Aydoğmuş; Şakir Bor (705-710).
Slightly Ni-rich, chemically homogeneous porous TiNi alloys having porosities in the range 59–81% have been produced using magnesium powder as pore forming agent. TiNi in the form of austenite, apart from a small amount of martensite, was the only phase present in the product. The processed alloys exhibited interconnected open pores spherical in shape and with an average pore size around 400 μm. Elastic modulus values observed to extend from 0.5 to 9 GPa depending on porosity content were comparable to that of cancellous bone.
Keywords: Intermetallics; Powder metallurgy; X-ray diffraction; Scanning electron microscopy;

Synthesis of photosensitive nanograined TiO2 thin films by SILAR method by U.M. Patil; K.V. Gurav; Oh-Shim Joo; C.D. Lokhande (711-715).
Nanocrystalline TiO2 thin films are deposited by simple successive ionic layer adsorption and reaction (SILAR) method on glass and fluorine-doped tin oxide (FTO)-coated glass substrate from aqueous solution. The as-deposited films are heat treated at 673 K for 2 h in air. The change in structural, morphological and optical properties are studied by means of X-ray diffraction (XRD), selected area electron diffraction (SAED), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), transmission electron microscopy (TEM) and UV–vis–NIR spectrophotometer. The results show that the SILAR method allows the formation of anatase, nanocrystalline, and porous TiO2 thin films. The heat-treated film showed conversion efficiency of 0.047% in photoelectrochemical cell with 1 M NaOH electrolyte.
Keywords: Thin film; Titanium dioxide (TiO2); Chemical synthesis; Optical properties; Photoelectrochemical properties;

In this paper, the synthesis of capacitor-grade tantalum (Ta) powder via the self-propagating high-temperature synthesis (SHS) method is described. In addition, the sintering aspects and electrical characteristics of the powder are discussed. Ta powder was prepared via the combustion of a Ta2O5xMg–kNaCl mixture, under argon pressure. The morphology and size of the final powder particles was controlled by adjusting the Mg–NaCl concentration. The final powder particles had nodular shapes and sizes ranging from 0.1 to 0.5 μm. A leakage current of a sintered Ta sample containing the smallest particle size was 10 μA; its capacitance was 92,738 CV, when a 40-V voltage was applied to the sample.
Keywords: Ta; SHS; Capacitor;

The self-propagating high-temperature synthesis (SHS) of 0–40 wt.% ZrB2 or 40 wt.% TiB2 reinforced Ni–Al matrix composite powders has been investigated. The SHS reactions were conducted starting from elemental powders of Zr, Ti, Ni, Al, and amorphous B. For all initial compositions, the product contained only the NiAl and ZrB2 or TiB2 compounds without any trace of cross-reaction phases. The powder, obtained by grinding the reacted pellet, contained ZrB2 or TiB2 homogeneously dispersed in the NiAl matrix. The dimension and distribution of the reinforcement phase make the powder suitable as precursor for thermal spray applications. After sintering of the composite powder up to 85% of theoretical density, microhardness was measured. The microhardness of pure NiAl was 394 ± 37 HV0.2. It increased considerably by the addition of the boride phases. Samples containing 40 wt.% ZrB2 and TiB2 attained values of 812 ± 94 and 967 ± 104 HV0.2, respectively.
Keywords: Coating materials; Composite materials; Inorganic materials; Chemical synthesis; Scanning electron microscopy; SEM;

Wear behaviour of nitric acid passivated cp Ti and Ti6Al4V by M. Masmoudi; M. Assoul; M. Wery; R. Abdelhedi; F. El Halouani; G. Monteil (726-730).
The aim of this paper is to examine the wear behaviour of passivated materials (cp Ti and Ti6Al4V), under various solicitation conditions. An analytical method (fractional factorial design 24–1) has been developed. To detect the significant variables, Lenth's individual contrast method was applied. The two factors, material and hydrogen peroxide had a marked effect on the wear behaviour. Whereas, the effects of the linear speed and the normal load (consequently the contact pressure) were less important. The wear rate was higher in case of Ti6Al4V alloys than that in the cp Ti sample. The effect of hydrogen peroxide tends to decrease the wear rate. The presence of this oxidant in the solution was generated chemical reactions with material and/or the wear particles.
Keywords: Titanium; Hydrogen peroxide; Wear; Fractional factorial design;

Principal component analysis (PCA) is used to investigate interrelationship among material properties of hydrides. Property data which consist of ∼200 compounds (binary and ternary metal hydrides) were analyzed. A comparative study was carried out among the metal properties with that of their hydrides. The observed decrease or increase of entropy, molar volume and specific heat of hydrides from that of the metals can be attributed to hydrogen bond formation, charge transfer and corresponding change in crystal structure.
Keywords: Metal hydrides; Energy storage materials; Thermodynamic properties; Metals and alloys;

Nanoparticles of strontium hexaferrite doped with Zr–Zn are synthesized by a chemical co-precipitation method. The crystallite sizes of 30–47 nm are small enough to obtain a suitable signal to noise ratio for application in the magnetic recording media. The temperature dependent DC resistivity of Zr–Zn doped samples shows metal-to-semiconductor transition in the temperature (T MS) range of 388–408 K. The Curie temperature, DC resistivity and activation energy for hopping decrease but the dielectric constant, dielectric loss and drift mobility increase by enhancing Zr–Zn content. With the substitution of Zr–Zn content of x  ≤ 0.4 the saturation magnetization, magnetic moment and remanence increase from 71 to 92 kA m−1, 11.2–13.6 μB and 55–59 kA m−1, respectively, while coercivity decreases from 137 to 34 kA m−1. With the improvement in the values of the above-mentioned parameters, the synthesized materials may be suitable for potential application in recording media.
Keywords: Nanomaterials; Magnetic properties; X-ray diffraction; Oxide materials; Co-precipitation method;

Characterization of YIG nanopowders by mechanochemical synthesis by Ayhan Mergen; Anjum Qureshi (741-744).
Yittrium iron garnet, Y3Fe5O12 (YIG), is a material used widely in electronic devices for the microwave region as well as the magnetic bubble domain-type memories. Yittrium iron garnet (Y3Fe5O12) was produced by mechanochemical synthesis from Y2O3 and Fe2O3 with a particle size of around 150 nm. Dense ceramics with theoretical density of around 95% was obtained from mechanochemically activated powders after sintering at 1425 °C for 10 h without calcination step. Ferro-magnetic resonance (FMR) spectrum and microwave absorption spectrum of the YIG nanoparticles were studied at different frequencies and magnetic fields. The signal exhibits a resonance character at each frequency. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing frequency. The dielectric properties of YIG pellets produced from nanopowder was studied over a wide range of frequency and as a function of temperature. It was observed that the dielectric constant, dielectric loss and electrical conductivity gradually increase with temperature.
Keywords: Yittrium iron garnet; Y3Fe5O12 (YIG); Dielectric properties; Magnetic properties;

Comparing the dynamic and thermodynamic behaviors of Al86Ni9-La5/(La0.5Ce0.5)5 amorphous alloys by G.H. Li; W.M. Wang; X.F. Bian; J.T. Zhang; R. Li; L. Wang (745-749).
The dynamic viscosities and thermodynamic dilatometric behaviors of Al86Ni9La5 and Al86Ni9(La0.5Ce0.5)5 amorphous alloys were investigated using viscometer, differential scanning calorimetry (DSC) and conventional dilatometer. Comparing with Al86Ni9La5 alloy, Al86Ni9(La0.5Ce0.5)5 alloy exhibits a larger viscosity and a larger average thermal expansion coefficient in the linear expansion zone (α exp). The viscosity and thermal expansion data suggest that the partial substitution La by Ce decreases the quantity of free volume in Al–Ni–La system by improving the continuous degree of atomic size, which leads to the improvement of glass forming ability.
Keywords: Amorphous materials; Liquid quenching; Thermal analysis;

Fe–36 wt.%Ni alloy film was prepared through direct current electrodeposition to investigate the effect of 2-butyne-1,4-diol(BD) on the microstructure and internal stress of the deposited films. The deposits composition was not affected by the addition of BD when its concentration in the electrolyte was above 0.2 g/L. All the film surfaces exhibited a flat and compact appearance. X-ray diffraction analyse revealed a phase of solid solution of iron in face centered cubic nickel, and the addition of BD caused strong (1 1 1) texture. The measurement of internal stresses showed a decrease of compressive stress with addition of BD in the electrolyte, and at the concentration of 0.4 g/L, tensile stress showed up in the film and caused some micro-cracks parallel to the surface.
Keywords: 2-Butyne-1,4-diol; Electrodeposition; Fe–Ni film; Internal stress;

The electronic structures of LiSi, NaSi, RbSi, and CsSi have been calculated using a first-principle pseudopotential method to clarify the possibility of band-gap broadening of BaSi2 by alloying with alkali metals.All of them are found to be semiconductors with the calculated indirect band gaps of 1.17 eV (LiSi) and 1.24 eV (NaSi) or the calculated direct band gaps of 1.32 eV (KSi), 1.38 eV (RbSi), and 1.66 eV (CsSi). The general tendency that the gap values of these ionic semiconductors are increased as their ionicities are increased and alkali metal incorporation into BaSi2 will be hopeful to broaden its band-gap.
Keywords: Semiconductors; Intermetallics; Electronic band structure;

Transmission electron microscopy investigation of the micro-defects in Czochralski silicon by Jin Xu; Weiqiang Wang; Deren Yang; H.J. Moeller (758-762).
The influence of rapid thermal annealing (RTA) on the formation of oxygen precipitates and extended defects has been investigated by transmission electron microscopy (TEM) in heavily and lightly boron-doped Czochralski (Cz) silicon, respectively. It reveals that for the heavily doped specimen undergo RTA pre-annealing, there are oxygen precipitates with high density generated, accompanied with the stacking faults, while for the specimen without RTA pre-annealing, dislocation generated; as for the lightly doped specimen, it found that there are dislocations generated in the specimen undergo RTA pre-annealing, while oxygen precipitate-related dislocations generated in the specimen without RTA pre-annealing, respectively. The main reason is due to the enhancement of oxygen precipitation by heavy boron doping and the increment of vacancy concentration in the bulk injected into the bulk by RTA pre-annealing.
Keywords: Rapid thermal annealing; TEM; Czochralski silicon;

Crystallization and corrosion resistance of as-spun (Al86Ni9La5)98Zr2 amorphous alloy by J.G. Lin; W.W. Wang; X.Q. Wu; J.H. Lei; S. Yin (763-766).
(Al86Ni9La5)98Zr2 amorphous alloy ribbons were successfully prepared by using the melt spinning technique, and the crystallization behavior of the amorphous ribbons was investigated. The result indicated that the amorphous alloy exhibited a three-step crystallization process with crystallization stages starting at 545 K, 606 K and 641 K, respectively. By annealing treatment at the different temperatures, the samples with the different crystallization extents were obtained. The potentiodynamic polarization measurements on these samples revealed that the sample with the primary crystallization exhibited higher corrosion resistance than that of the as-spun amorphous ribbons, while the secondary and complete crystallization was detrimental to the corrosion resistance of the alloy.
Keywords: Al-based amorphous alloys; Heat treatment; Electrochemical corrosion;

Synthesis and properties of Li–Ti–O spinel (LiTi2O4) by C.Q. Feng; L. Li; Z.P. Guo; D.Q. Shi; R. Zeng; X.J. Zhu (767-770).
A simple method for preparing LiTi2O4 is reported in this paper. Characterization by the X-ray diffraction method indicated that the LiTi2O4 had formed with the spinel crystal structure. The particle size and shape of the compound were observed by scanning electron microscopy techniques. The superconducting and electrochemical properties of LiTi2O4 spinel have also been investigated. The results showed that this material is not only a superconductor with critical temperature, T c  = 13 K, but also a promising anode material, which showed discharge specific capacity (240 mAh g−1) and excellent cycling ability in the range of 3.00–0.01 V at certain current density (20 mA/g).
Keywords: Electrode materials; Superconductors; Chemical synthesis; X-ray diffraction; Electrochemical reactions;

A novel method has been used to synthesize samples in the Ca1−x La x Cu3Ti4−x Co x O12 system (x  = 0.10, 0.20 and 0.30) using solid TiO2 powder and metal nitrate solutions. X-ray powder diffraction analysis confirms the formation of single phase at 900 °C. SEM micrographs of the system confirmed the average grain size is 1–2 μm. Transmission electron microscopy has been employed to characterize the structure of resulting materials. Energy dispersive X-ray analysis (EDXA) confirms the stoichiometry of the synthesized materials. Dielectric constant and dielectric loss of the composition was found to be 2000 and 0.50 respectively at room temperature (1 kHz). AC conductivity of Ca1−x La x Cu3Ti4−x Co x O12 sample increases with increasing temperature, which shows semiconducting behavior of the materials.
Keywords: Electronic materials; Chemical synthesis; Thermogravimetric analysis; X-ray diffraction; Microstructure;

The paper describes the preparation and characterization of nano-size orthorhombic and monosilicate Nd2O3–SiO2 mixed oxides prepared by a sol–gel method. The phase separation in Nd2O3–SiO2 system on a subsequent heat treatment in air was also investigated at constant sintering temperature 850 °C with varying annealing time 5–20 h. Characterization was made by X-ray diffraction (XRD), Fourier transformation infrared (FTIR) and scanning electron microscopy (SEM). Mechanisms of neodymium clusters formation in densified silica matrix with respect to thermal treatment are discussed.
Keywords: Oxides; Nanostructures; Metals; Glasses; Elements;

The microwave dielectric properties and the microstructures of (1 −  x)CaTiO3xNd(Mg1/2Ti1/2)O3 ceramics prepared by the conventional solid-state route have been studied. Doping with 0.5 wt% ZnO can effectively promote the densification and the microwave dielectric properties of (1 −  x)CaTiO3xNd(Mg1/2Ti1/2)O3. The dielectric constant decreases from 145 to 30.5 as x varies from 0.1 to 1.0. In the (1 −  x)CaTiO3xNd(Mg1/2Ti1/2)O3 system, the microwave dielectric properties can be effectively controlled by varying the x value. The dielectric constant of 44, a Q  ×  f value of 43,800 GHz and a τ f value of 1.2 ppm/°C were obtained for 0.1CaTiO3–0.9Nd(Mg1/2Ti1/2)O3 ceramics sintered at 1325 °C for 4 h. A band-pass filter is designed and simulated using the proposed dielectric to study its performance.
Keywords: Dielectric properties; Microwave dielectric properties; X-ray;

Ti0.32Cr0.43V0.25 and LaNi5 were prepared independently by arc melting. These two alloys were made into composite as Ti0.32Cr0.43V0.25  +  x  wt% LaNi5 (with x    =   5, 10 and 20). In addition, an alloy of Ti–Cr–V with rare-earth elements La, Ce and Y were also prepared. These composite alloys were characterized for their structure and hydrogen storage characteristics. Phase analysis and microstructural studies were carried out using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. A Rietveld refinement for the alloy 80 wt% Ti0.32Cr0.43V0.25  + 20 wt% LaNi5 shows five phases assigned as two BCC, La2O3, VO2, and TiCr2. Hydrogen storage capacity and hydrogen plateau pressure were likely to be affected by the lattice parameter of BCC phase and the formation of secondary phases. The hydrogenation characteristics for these mixed compositions were investigated.
Keywords: Hydrogen absorbing materials; X-ray diffraction; Transmission electron microscopy; BCC alloys;

On tension–compression yield asymmetry in an extruded Mg–3Al–1Zn alloy by De Liang Yin; Jing Tao Wang; Jin Qiang Liu; Xiang Zhao (789-795).
The tension–compression yield asymmetry of an extruded Mg–3Al–1Zn alloy was examined by changing load directions and grain sizes in room-temperature mechanical tests. A criterion for the activation of deformation modes was proposed to analyze the effect of load direction on twinning activity. When the load angle was 45°, the twin area fractions after tension and compression resembled each other, and the corresponding ratio between compression yield stress and tension yield stress equaled 1.02. As the load direction was parallel or perpendicular to the extrusion axis, the yield stress and twinning activity in tension differed obviously from those in compression, resulting in marked tension–compression yield asymmetry. Although grain-coarsening promotes twinning in tension along extrusion axis, it cannot reduce the yield asymmetry. Further, the contributions of twinning to strain during yield deformation were evaluated based on the quantitative statistic of twin area fraction.
Keywords: Asymmetry; Twinning; Grain size; Magnesium alloy; Mechanical property;

Microstructure and electromagnetic characteristics of Ni nanoparticle film coated carbon microcoils by Hui Bi; Kai-Chang Kou; Kostya (Ken) Ostrikov; Lu-Ke Yan; Zhi-Chao Wang (796-800).
Carbon microcoils (CMCs) have been coated with a Ni nanoparticle film using an electroless plating process. The morphology, the elemental composition and the phases in the coating layer, complex permittivity and permeability of the CMCs and Ni-coated CMCs were, respectively, investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and microwave vector network analysis at room temperature. A homogeneous dispersion of Ni nanoparticles on the outer surface of the CMCs was obtained, with a mean particle size of ∼34.4 nm and the phosphorus content of about 8.5 wt%. When comparing the coated and uncoated CMC samples, the real (ɛ′) and imaginary (ɛ″) part of the complex permittivity as well as dielectric dissipation factor (tgδ ɛ  =  ɛ″/ɛ′) of the Ni-coated CMCs were much smaller, while the real (μ′) and imaginary (μ″) part of the complex permeability and the magnetic dissipation factor ( t g σ μ = μ ″ / μ ′ ) were larger. The enhanced microwave absorption of Ni-coated CMCs resulted from stronger dielectric and magnetic losses. In contrast, the microwave absorption of uncoated CMCs was mainly attributed to the dielectric rather than magnetic losses.
Keywords: Carbon microcoils; Nanocomposites; Magnetic properties; Scanning electron microscopy; Chemical vapor deposition;

Si4+ and B3+ were doped into the spinel block of blue-emitting BaMgAl10O17:Eu2+ phosphor. Their photoluminescence, such as emission characteristic and thermal stability, were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The results showed that proper quantities of Si4+ or B3+ doping could obviously improve the emission intensity. However, the thermal stability of Si4+ or B3+ doped phosphors was worse than that of undoped samples. Based on lattice defect theory, the mechanisms of these interesting phenomena were discussed and explained, which revealed that the thermal degradation of BaMgAl10O17:Eu2+ had great correlation with the lattice environment.
Keywords: Phosphor; Optical properties; Luminescence;

The charge ordering (CO) transition in polycrystalline La1/3Sr2/3Fe1−x Cr x O3 (x  = 0, 0.015, 0.025, 0.05) has been studied by measuring the low temperature magnetization, resistivity and longitudinal ultrasonic velocity (V l). It is found that with increasing Cr content, the resistivity increases and the charge ordering transition temperature T CO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in V l above T CO and a dramatic stiffening below T CO are observed. This abnormal elastic softening above T CO can be described well by the mean-field theory, which indicates that the Jahn–Teller effect plays an important role for the charge ordering transition in La1/3Sr2/3Fe1−x Cr x O3. Below T CO, another softening in V l is observed for x  = 0 sample, which is attributed to the breathing-type distortion of Fe–O octahedron. With Cr doping, this ultrasonic anomaly weakens. This behavior suggests that the charge disproportionation (CD) transition is suppressed by the Cr substitution.
Keywords: Rare earth compounds and compounds; Oxide materials; Electron–phonon interaction; Ultrasonic;

Grain refinement by AlN particles in Mg–Al based alloys by H.M. Fu; M.-X. Zhang; D. Qiu; P.M. Kelly; J.A. Taylor (809-812).
AlN has been identified as a potential grain refiner for magnesium alloys using the edge-to-edge matching calculations. Experimental results indicate that the maximum grain refining efficiency of AlN in Mg–Al alloys occurs in samples cast from a melt temperature of 765 °C. Under these conditions, an addition of 0.5 wt% AlN reduces the grain size of Mg–3 wt% Al alloy from 450 to 120 μm. No further reduction is observed when more AlN is added to the melt.
Keywords: Metals and alloys; Casting; Magnesium alloys; Grain refinement; AlN; Edge-to-edge matching model;

Luminescent characteristics of LiBaBO3:Tb3+ green phosphor for white LED by Panlai Li; Libin Pang; Zhijun Wang; Zhiping Yang; Qinglin Guo; Xu Li (813-815).
A novel green phosphor, LiBaBO3:Tb3+, has been developed for white light-emitting diodes (LEDs). The phosphor was prepared by using solid state reaction and its luminescent characteristics were investigated. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (UV) 368 and 381 nm light, and exhibit a satisfactory green performance (544 nm), nicely, fitting in with the widely applied UV LED chip.
Keywords: Phosphor; Luminescence;

A network structure of carbon nanotubes (CNTs) and nickel/alumina (CNT(Ni)–Al2O3) composite particles was developed, which involved producing a Ni(OH)2/Al precursor, followed by calcination in air and reduction in hydrogen to yield a Ni/Al2O3 catalyst with a network structure, which was used to synthesize nanotubes by chemical vapor deposition. The CNT(Ni)–Al2O3 hybrid was then employed to produce alumina matrix composites by spark plasma sintering of the CNT(Ni)–Al2O3 composite powder. Microstructure and mechanical properties of the composites were characterized. The results showed that the CNTs dispersed homogenously and bonded strongly with the alumina matrix and the composites showed a 67% increase in fracture toughness and 17.5% increase in hardness compared to monolithic alumina. The improvement of the fracture toughness and hardness was attributed to the network structure of CNT(Ni)–Al2O3, which ensured homogenously dispersed CNTs in the matrix and tight interfacial bonding between CNTs and alumina matrix, and thus led to a good stress transfer between the nanotube and alumina matrix.
Keywords: Composite materials; Inorganic materials; Chemical synthesis; Mechanical properties;

The defect volumes in LiH for the formation of a Schottky defect as well as for the cation vacancy migration are estimated for the first time. Their values are found to be larger and smaller, respectively, than the molecular volume. The calculation is based on the equation of state obtained from single-crystal synchrotron X-ray diffraction measurements on solid 7LiH up to 36 GPa, by relying on an interconnection between defect Gibbs energy and bulk elastic data.
Keywords: Schottky defect; Cation vacancy; High pressure; Bulk modulus;

β-Co(OH)2 hexagonal nanoplates with a diameter of 200–400 nm and a thickness of 30–50 nm have been synthesized successfully by a template and surfactant-free hydrothermal route in a very simple system composed only of water, CoCl2 and NaOH, and many of them are regular hexagons with the angles of adjacent edges of 120°. This method is high yield, simple and environmentally benign. According to the systematical investigation of the reaction parameters (temperature, time and the concentration of NaOH), the optimal conditions to β-Co(OH)2 hexagonal nanoplates were concluded, including the temperature of 120 °C, the hydrothermal time of 3 h and the NaOH dosage of 5 mmol. A dissolution–recrystallization mechanism was put forward. Furthermore, the as-obtained Co(OH)2 hexagonal nanoplates can be easily converted into porous Co3O4 nanoplates by calcining Co(OH)2 nanoplates in air at 500 °C for 2 h.
Keywords: Electrode materials; Nanostructured materials; Chemical synthesis;

The different fracture features developed during quasi-static and dynamic compressive deformation of Mg-based bulk metallic glass and composite reinforced by SiC particulate were investigated. Mg-based amorphous glass fractures on one major plane and shows a planar and smooth fracture surface upon quasi-static loading. The fracture surface of composite is rough, which is composed of a great deal of small mirror planes in quasi-static tests. Rugged fracture surfaces were observed both in Mg-based amorphous glass and composite during dynamic deformation. A large area of molten liquid spreads over the whole fracture surface, indicating more severe temperature rise occurs during dynamic deformation. When encountering SiC particulates during propagation, cracks cut through (sometimes being stopped inside the particulate) or bypass the particle. The fact that cracks cut through or bypass particles reflects the strong bonding at the particle–matrix interfaces and the effective load transfer from matrix to the reinforcing particles. The block function to crack propagation due to the presence of particles is expected for shear bands before cracking initiates inside the shear bands, avoiding the formation of major shear band and the catastrophic failure likely.
Keywords: Metallic glasses; Composite; Fracture surface;

High-temperature dynamic compressive properties of two monolithic Zr-based amorphous alloys by Yang Gon Kim; Dong-Geun Lee; Byoungchul Hwang; Sunghak Lee (831-835).
This study investigated high-temperature dynamic compressive properties of two Zr-based monolithic amorphous alloys. Dynamic compressive tests were conducted in the temperature range from room-temperature to 380 °C using a compressive Kolsky bar, and then the test data were analyzed in relation to microstructure and fracture mode. Both the maximum compressive stress and total strain of the two amorphous alloys decreased with increasing test temperature because shear bands could propagate rapidly as the adiabatic heating effect was added at high-temperatures. Above the glass transition temperature (T g), the total strain decreased more abruptly than the total strain measured between room-temperature and 300 °C because of the crystallization of amorphous phases. The alloy having lower T g and larger ΔT showed the better total strain because of the lower viscosity, which could favorably affect the ductility.
Keywords: Zr-based amorphous alloy; Dynamic compression Kolsky bar; Glass transition temperature;

The effect of annealing temperature on the microstructure, magnetic and mechanical properties of MgB2 superconducting samples has been studied. The study consists of XRD, SEM, ac susceptibility, Vickers microhardness and density measurements. These measurements indicated that the grain sizes, lattice parameters, density, and critical transition temperature increase and the grain connectivity are improved with increasing the annealing temperature up to 850 °C. It was also found that the Vickers microhardness of the samples was dependent on the annealing temperature and applied load. In addition, we calculate the load dependent mechanical properties of the samples using different model. We have discussed the possible reasons for the observed improvements in microstructure, superconducting and mechanical properties due to annealing temperature.
Keywords: Annealing temperature; Microstructure; Lattice parameters; ac Susceptibility; Microhardness; Fracture toughness; Young's modulus; Yield strength;

Microwave dielectric properties of (Mg0.95Co0.05)TiO3–(Na0.5Nd0.5)TiO3 ceramic system by Cheng-Liang Huang; Jhih-Yong Chen; Yen-Hsing Wang (842-846).
The microwave dielectric properties and the microstructures of the (1 −  x)(Mg0.95Co0.05)TiO3x(Na0.5Nd0.5)TiO3 (0.1 ≤  x  ≤ 0.18) ceramic system have been investigated. The two phase system was confirmed by XRD and EDX analysis throughout the entire experimental range. In this system, the microwave dielectric properties can be effectively controlled by varying the x value. The dielectric constant ranged from 18.3 to 25.4 as the x varies from 0.1 to 0.18. With the increase of sintering temperature, the Q  ×  f increased to a maximum and decreased thereafter. A maximum Q  ×  f  ∼ 112,000 GHz (where f  = 8.6 GHz, is the resonant frequency) was achieved for samples with x  = 0.1. For practical applications, a new microwave dielectric material, 0.84(Mg0.95Co0.05)TiO3–0.16(Na0.5Nd0.5)TiO3, is suggested and possesses a good combination of dielectric properties: ɛ r  ∼ 24.39, Q  ×  f  ∼ 70,000 GHz, τ f  ∼ 1.6 ppm/°C. It is proposed as a suitable candidate dielectric for GPS patch antennas and passive components in wireless communication system.
Keywords: Crystal growth; Dielectric response;

Nanocrystalline W-type hexaferrites of nominal stoichiometry of BaZn2Cr x Fe16−x O27 (x  ≤ 1) have been synthesized by the chemical co-precipitation method and their structural, electrical and magnetic properties have been investigated. In most of the published work, synthesis of a single W-type hexagonal phase is reported at high annealing temperatures of 1300–1573 K. However, we have attempted to synthesize it at lower annealing temperatures of 1223 K. The X-ray diffraction (XRD) patterns conform to the standard single phase of the hexagonal W-type structure. The elemental composition estimated from the energy dispersive X-ray fluorescence (ED-XRF) analysis is in good agreement with the nominal composition. Surface morphological studies are carried out using scanning electron microscopy (SEM) analysis. The DC electrical resistivity (ρ) and AC magnetic susceptibility (χ) studies are performed in a temperature range of 300–663 K and 423–663 K, respectively. We are able to enhance the room temperature resistivity (ρ RT) of BaZn2Fe16O27 by doping it with Cr to the order of 109  Ω cm which is higher than those previously reported for the W-type hexaferrites (103–107  Ω cm). The dielectric constant (ɛ′) and dielectric loss (tan  δ) decrease with the frequency, on the other hand both these parameters are enhanced by doping the material with Cr. The enhancements in the above mentioned parameters make them promising for use at high frequencies in order to reduce eddy current losses, in radar absorbing purposes and for electromagnetic interference attenuation. All the samples show a metal to semiconductor transition at a temperature (T M–S) that varies with chromium concentration. Dielectric studies show that the electrical conduction in these materials is due to the collective contribution of electrons as well as of the holes.
Keywords: Semiconductors; Nanostructured materials; Dielectric response; Magnetic measurements; Hexaferrites;

Lead magnesium niobate–lead titanate (0.80Pb(Mg1/3Nb2/3)O3–0.20PbTiO3, PMN–PT) thick films on platinum metallic foils were successfully fabricated by electrophoretic deposition (EPD). The room temperature relative dielectric constant and the maximum relative dielectric constant were 4645 and 25,640 at 1 kHz, respectively. The relaxor nature of PMN–PT thick films was studied in terms of diffused phase transition along with frequency dispersion of temperature of dielectric maximum (T m). Deviation from Curie–Weiss behavior and temperature evolution of the local order parameter were found in the films. The degree of relaxation obtained from the modified Curie–Weiss law strongly suggests the relaxor behavior. Vögel–Fulcher relationship was used to analyze the frequency dependence of temperature of dielectric maximum (T m).
Keywords: PMN–PT; Relaxor; Dielectric response; Electrophoresis deposition;

Synthesis and characterization of CBS glass/ceramic composites for LTCC application by Guo-hua Chen; Lin-jiang Tang; Jun Cheng; Min-hong Jiang (858-862).
CBS (CaO–B2O3–SiO2) glass/cordierite (Mg2Al4Si5O18) ceramic composites were prepared using standard ceramic process. Effects of cordierite on crystallization behavior of the CBS glass powder were investigated. Results showed that crystalline phases like pseudowollastonite (CaSiO3) and quartz (SiO2) were formed during the firing of glass alone. For the composites with ≥45 vol. % cordierite at 780–1200 °C, the above crystalline phases were completely prevented but new phase of anorthite (CaAl2Si2O8) was formed. For all the composites, the intensity of peaks characterizing cordierite gradually decreases and that of characterizing anorthite synchronously enhances with increasing sintering temperature. Microstructural changes of all the samples with sintering temperature were in good agreement with the relative density and an optimum firing temperature for maximum densification existed for each glass/ceramic ratio. The thermal expansion coefficient (TEC) of the composites decreases with increase in cordierite ceramic volume percent. The TEC of all the composites was in the range of 2.2 × 10−6  K−1 to 5.2 × 10−6  K−1. The dielectric constant of the fabricated composites was between 5.2 and 6.2. The precipitation of anorthite has no bad effect on the dielectric constant and the TEC of the resulting composites because anorthite has low dielectric constant (6.2) and low thermal expansion coefficient (4.82 × 10−6  K−1). The prepared glass/ceramic composites were well suited for LTCC application.
Keywords: Glass–ceramics; Sintering; Dielectric properties; Thermal expansion; X-ray diffraction; SEM;

The interface between two dental alloys (Pd–Cu–Ga, Pd–Ga) cast-to a prefabricated gold cylinder in two thicknesses (1, 2 mm) was investigated. Specimens were observed in optical and scanning electron microscopes. Line scan microanalysis by EDS was performed and polarization curves were taken. Gold cylinders shape was preserved. Characteristic elongated grains were detected at the gold cylinder alloy. The boundaries between the cylinder and the cast-to alloys were distinct. The 2 mm thick Pd–Ga alloy cast to the gold cylinder revealed high porosity at the interface, while the rest of the subgroups showed no or negligible porosity. Line scan analysis revealed the gradual diffusion of the main elements of each alloy in the structure of the gold cylinder and vice-versa in a 3–5 μm zone. Corrosion behaviour was estimated by cyclic polarization tests in 1 M lactic acid. The polarization curves showed negative hysteresis. In the reverse anodic scan the current density was less than that for the forward scan. This fact confirms that all the tested materials are not susceptible to corrosion in 1 M lactic acid.
Keywords: Dental alloys; Microstructure; Corrosion; Metallography; Scanning electron microscopy (SEM);

Effect of platinum present in multi-element nanoparticles on methanol oxidation by Chih-Fang Tsai; Kung-Yu Yeh; Pu-Wei Wu; Yi-Fan Hsieh; Pang Lin (868-871).
Nanoparticles of Pt x Fe(100−x)/5Co(100−x)/5Ni(100−x)/5Cu(100−x)/5Ag(100−x)/5 (x  = 22, 29, 52, 56) were prepared by the sputter depositions on pretreated carbon clothes with their electrocatalytic abilities for the methanol oxidation investigated. XRD analysis of the deposited nanoparticles indicated crystalline fcc phases and SEM images revealed apparent growths of nanoparticulate nodules. Their average sizes were found to increase with the deposition time. Cyclic voltammetry of the deposited samples demonstrated enhancements in the current responses with increasing Pt amount and deposition time. In mass activity, the Pt52Fe11Co10Ni11Cu10Ag8 exhibited the highest values of 462–504 mA/mg. Identical process was conducted to fabricate electrodes with sputtered Pt and Pt43Ru57. In comparison, the Pt52Fe11Co10Ni11Cu10Ag8 showed moderate improvements over that of Pt but was still outperformed by the Pt43Ru57.
Keywords: Fuel cells; Nanostructured materials; Catalysis; Methanol oxidation;

Solvothermal synthesis and optical properties of single-crystal ZnS nanorods by Hongmei Wang; Zhe Chen; Qiong Cheng; Lixia Yuan (872-875).
High-resolution transmission electron microscopy (HRTEM) was performed on a single nanorod of the sample. The crystal plane space is calculated to be 0.313 nm, which is consistent with the (0 0 2) planes of the wurtzite ZnS. The HRTEM image reveals that the as-prepared ZnS nanorod grows along the [0 0 1] direction.Pure and uniform hexagonal-phase ZnS nanorods with quantum confinement effect were synthesized by solvothermal method. The as-prepared product had been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and high-resolution transmission electron microscopy (HRTEM). Photoluminescence spectrum (PL) and UV–vis absorption spectrum were used to investigate the optical properties of ZnS nanorods. The strong emission peak centered at 425 nm in PL spectrum could be attributed to the electron–hole recombination from internal vacancies for Zn and S atoms.
Keywords: Solvothermal; ZnS; Nanostructure; Single crystal; Optical properties;

Synthesis of core–shell α-Fe2O3 hollow micro-spheres by a simple two-step process by Shibing Ni; Shumei Lin; Qingtao Pan; Feng Yang; Kai Huang; Xiaoyi Wang; Deyan He (876-879).
Core–shell Fe2O3 hollow micro-spheres have been fabricated by a simple two-step method. Firstly, compound of carbon and iron hydrate were synthesized by hydrothermal process. The obtained products were characterized by X-ray diffraction (XRD), which exhibit the diffraction peaks of orthorhombic phase of iron oxide hydroxide. Energy dispersive X-ray spectroscopy (EDS) measurement indicates the existence of carbon. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results show flake-based urchin-like architecture. Secondly, core–shell hollow micro-spheres were obtained by subsequent annealing process. XRD pattern of the final sample is well in agreement with the standard pattern of the hexagonal rhomb-centered α-Fe2O3. FE-SEM and TEM images reveal that those hollow spheres are of core–shell architecture with holes on the surfaces. Magnetic hysteresis measurement carried out on vibrant sample magnetometer (VSM) shows weak ferromagnetic property at room temperature. On the basis of the obtained experimental results, the possible formation mechanism was discussed.
Keywords: Nanostructures; Crystal growth; Magnetic measurements;

Author Index (881-883).

Subject Index (884-896).