Materials Letters (v.61, #27)

Lattice dynamical calculations for the Ta–W alloys by Engin Deligöz; Kemal Çolakoğlu; Yasemin Çiftçi (4867-4871).
Lattice dynamical calculations are performed on Ta–W alloys with bcc structure in various concentrations. We assume ion–ion interaction through the improved third-neighbor Clark–Gazis–Wallis (CGW) model. The theory has been applied to compute the dispersion curves, frequency spectra and lattice specific heat of the studied alloys. The obtained results are in good agreement with the available experimental ones.
Keywords: Lattice dynamics; CGW model; Specific heat;

An electrical discharge machine (EDM) can be used to produce Uranium Carbide (UC) microspheres. This material is useful for dispersed nuclear fuel fabrication. To obtain empirical data about the process parameters for UC modeling, 304 stainless steel (304 SS) was used to produce microspheres. Particle size effects were analyzed via three parameters; arc intensity, dielectric medium, and pulse width. Results indicate that the size and yield of the particles are dependent on all three parameters. The yield of larger particles increased with increasing arc current. Particle size distribution decreased with decreasing pulse width.
Keywords: EDM; Arc intensity; Microspheres; EDM parameters; Size distribution;

Influence of quenching rate on the crystallization behaviors of Mg63Ni22Pr15 metallic glass by Feng Xu; Yulei Du; Ping Gao; Zhida Han; Guang Chen (4875-4878).
The influence of the quenching rate (from 5 m/s to 40 m/s) on the crystallization behaviors of melt-spun Mg63Ni22Pr15 metallic glasses has been studied. The isochronal differential scanning calorimeter (DSC) measurement at 20 K/min shows that the transition temperatures increase with the quenching rate, while the parameters of the glass-forming ability keep constant. The kinetics of isothermal crystallization performed at 481 K within the supercooled liquid region is discussed with some nucleation and growth models. The fittings show that with decreasing quenching rate, the quenched-in nucleation becomes more important and even dominant in the crystallization process.
Keywords: Metals and alloys; Kinetics; Metallic glasses; Isothermal crystallization; Quenched-in nuclei;

Electrical and magnetic properties of orthorhombic Pr2/3Ba1/3MnO3 (PBMO) and La2/3Ca1/3MnO3 (LCMO) manganites with considerable difference in variance factors (σ 2) are reported here. PBMO with higher variance exhibits distinct intrinsic (due to grains) and extrinsic (due to grain boundaries) transitions in the resistivity behaviour. Extrinsic effects, however, are not observed in the lower σ 2 LCMO system. Low field magnetoresistivity (LFMR) data also substantiate these results. Increase in the density of states obtained through Mott's 3-D variable range hopping mechanism in the paramagnetic insulating regime indicates the suppression of magnetic domain scattering with applied magnetic field. Ferromagnetic metallic regime below the extrinsic transition in PBMO seems to emanate from the electron–magnon scattering process. LFMR at 77 K also points towards the higher canting of spins in the vicinity of grain boundary regions in PBMO compared to that in LCMO.
Keywords: Manganites; Grain boundary effects; Low field magnetoresistivity (LFMR); Variable range hopping (VRH); Electron–magnon scattering;

The microstructure and orientation relationships of ZK60A magnesium alloy matrix composite reinforced with SiC whiskers and B4C particles have been studied by means of transmission electron microscopy and high-resolution electron microscopy. MgO nanocrystalline particles are formed at SiC/Mg interfaces with a cube-on-cube orientation relationship with SiC whiskers. MgB2 nanorods are formed near the B4C particles. Two types of orientation relationships between the SiC whisker and Mg are observed, which are [1¯11]SiC|| [0001]Mg and (022¯)SiC|| (112¯0)Mg, and [1¯11]SiC|| [112¯0]Mg and (022¯)SiC|| (011¯2)Mg. Geometrically, [1¯11]SiC|| [0001]Mg and (022¯)SiC|| (112¯0)Mg is more favorable than [1¯11]SiC|| [112¯0]Mg and (022¯)SiC|| (011¯2)Mg.
Keywords: Composite materials; Microstructure; Electron microscopy; Orientation relationship;

Synthesis of inorganic fullerene-like MoS2 nanoparticles by a facile method by Kai Du; Wuyou Fu; Ronghui Wei; Haibin Yang; Shikai Liu; Shidan Yu; Guangtian Zou (4887-4889).
A facile and low-cost synthesis route was used to synthesize inorganic fullerene-like (IF) MoS2 nanoparticles by reaction of sulfur powder and ammonium molybdate in a hydrogen atmosphere at 600 °C. As-synthesized IF-MoS2 nanoparticles are of a closed hollow cage structure with size of 10–20 nm. Nanowires and nanotubes were also obtained at the same annealing temperature. The composition, structure, and morphology of the products were characterized by XRD, Raman, and TEM and the possible growth mechanism is proposed.
Keywords: Fullerenes; Nanomaterials; MoS2; Hollow cage; Ammonium molybdate;

Multi-petals ZnO nano-structure has been directly prepared through a facile solution route with β-cyclodextrin (β-CD) assistance. The product was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicate that this ZnO nano-structure consists of several petals, and each petal is composed of many little rods. The rods prefer to grow along the [0001] direction (+c axis) and lay parallel, and β-CD plays a crucial role in forming such novel structure. If not using β-CD in the preparation process, only larger rods could be obtained. Furthermore, the possible formation mechanism for this multi-petals nano-structure is also discussed.
Keywords: ZnO; Nano-materials; Semi-conductors; Cyclodextrin;

A simple polyol method was developed to synthesize uniform sphere-like Co3O4 nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co3O4 nanocrystals were spherical with the crystallite size in the range of 90–110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co3O4 nanocrystals. The magnetic properties of the Co3O4 nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.
Keywords: Nanomaterials; Magnetic materials; Co3O4; Sphere-like; Magnetization;

Microstructure and electric properties of (104)/(014)-oriented Bi3.15Nd0.85Ti3O12 films on Pt (111)/Ti/SiO2/Si by sol–gel method by X.Q. Chen; Y. Qiao; X.L. Liu; C.J. Lu; Gwenael Le Rhun; Stephan Senz; Dietrich Hesse (4897-4900).
Bi3.15Nd0.85Ti3O12 (BNdT) thin films with predominant (104)/(014) orientation were fabricated directly on (111)Pt/Ti/SiO2/Si substrates through a sol–gel process. The volume fraction of (104)/(014)-oriented grains in the film was estimated to be about 65% according to X-ray pole figure. The BNdT film is dense and uniform and consists of columnar grains penetrating the whole film thickness. The (104)/(014)-oriented BNdT film capacitors showed excellent ferroelectric properties with 2P r  = 46.4 μC/cm2 and E c  ≈ 140 kV/cm. The films also exhibit excellent piezoelectric property, with high piezoelectric coefficient d 33  ≈ 17 pm/V.
Keywords: Ferroelectrics; Thin film; Orientation; Piezoelectricity;

Amorphous Fe78Si9B13/nano-Ni laminated composite was prepared by electrodeposition method. The tensile properties of laminated composite at room temperature were examined. The laminated composite exhibits a very high tensile strength and reasonable tensile elongation. This is attributed to a good bonding between amorphous Fe78Si9B13 layer and nano-Ni layers. The amorphous layer can deform in conformity with Ni layers and be significantly stretched without fracture. The apparent surface energy γ f of amorphous Fe78Si9B13 ribbon in the laminated composite is 7 times larger than γ f of amorphous ribbon in monolithic form. The isostrain model may be insufficient to explain the tensile behavior of the laminated composite.
Keywords: Amorphous Fe78Si9B13; Nano-Ni; Electrodeposition; Multilayer structure; Mechanical properties;

A facile synthetic route to aqueous dispersions of silver nanoparticles by Tom Hasell; Jixin Yang; Wenxin Wang; Paul D. Brown; Steven M. Howdle (4906-4910).
Stable aqueous dispersions of silver nanoparticles have been synthesized from an organometallic precursor dissolved in an organic phase. Hydrogen gas is used to reduce the precursor to form silver nanoparticles which spontaneously transfer into an immiscible aqueous phase where they are stabilized. This route provides a simple pathway for the preparation of aqueous nanoparticle solutions and avoids production of the inorganic ions that are usually associated with aqueous methods. The effectiveness of a variety of aqueous stabilizing agents is evaluated. All products show plasmon absorption bands characteristic of silver nanoparticles and transmission electron microscopy reveals most particles to be below 40 nm in diameter.
Keywords: Nanomaterials; Optical materials and properties; Polymers; TEM; Silver nanoparticles;

Structuring of multi-layered spherulites in aryl polyester of poly(trimethylene terephthalate) (PTT) by stepwise crystallization was attempted. Characterization of feasibility was performed by polarized-light microscopy (POM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). Two- or three-layered spherulites could be developed in PTT by subjecting to stepwise crystallization. Sequence and number of layers in spherulites can be designed by altering the steps of temperatures with proper holding time. Time must be allocated properly in the multiple steps if three different textures are to be structured into one single PTT spherulite by stepwise crystallization. Coexistence of multiple lamellar thicknesses and various degrees of crystal perfection were supported by DSC results. The various crystalline regions of the layered spherulites in PTT develop upon stepwise crystallization exhibit the same unit cell as demonstrated by WAXD crystallographs.
Keywords: Poly(trimethylene terephthalate) (PTT); Ring bands; Composite spherulites; Multi-layer core–shell structures;

This letter reports the synthesis of carbon nanotubes and diamond-like carbon films using cathodic micro-arc discharge in aqueous solutions. The conditions and mechanisms for the growth of these structures were briefly discussed based on the experimental observations.
Keywords: Nano-materials; Carbon nanotubes; Diamond-like carbon; Cathodic micro-arc discharge;

Preparation and properties of Ti/SnO2–Sb2O5 electrodes by electrodeposition by Hai-yang Ding; Yu-jie Feng; Jun-feng Liu (4920-4923).
Sb and Sn coatings were deposited on Ti substrate by the method of cathode deposition, and the Ti/SnO2–Sb2O5 electrodes were obtained by annealing at different temperatures for 3 h. Ti/SnO2–Sb2O5 coating was characterized using technique such as X-ray diffraction (XRD), and scanning electron microscopy (SEM). Ti/SnO2–Sb2O5 electrode calcined at 550 °C exhibits the best catalytic capacity. Ti/SnO2–Sb2O5 electrode obtained by electrodeposition had longer service life and faster degradation capacity compared with that obtained by dip-coating. Accelerated service life tests were carried out in 0.5 mol L− 1 H2SO4 solution with the current density of 100 mA cm− 2. Service life of Ti/SnO2–Sb2O5 electrode prepared in present study was 15 h, and it was only 0.14 h for Ti/SnO2–Sb2O5 electrode obtained by dip-coating.
Keywords: X-ray techniques; Deposition; Thin films; SnO2; Phenol;

Synthesis and characterization of Ba2YSbO6 nanoparticles through a modified combustion process by C. Vijayakumar; H. Padma Kumar; Jijimon K. Thomas; P.R.S. Wariar; J. Koshy (4924-4927).
Nanoparticles of Yttrium Barium Antimonate (Ba2YSbO6), a complex perovskite ceramic oxide have been synthesized using an auto ignition combustion process for the first time. The particle size and properties of the nanocrystals have been characterized by X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba2YSbO6 and has a complex cubic perovskite (A2BB'O6) crystalline structure with lattice constant a  = 8.402 Å. Transmission electron microscopy study has shown that the particle size of the as-prepared powder was in the range 20–50 nm. The nanocrystals of Ba2YSbO6 synthesized by the combustion technique could be sintered to 97% of the theoretical density at a temperature of 1550 °C for 4 h. The combustion synthesis has a definite advantage that the phase pure Ba2YSbO6 nanopowder could be obtained by a single step process without the need of a calcination step.
Keywords: Nanocrystals; Ceramics; Combustion; Sintering;

A novel soft magnetic nanocomposite with FeCo particles encapsulated by amorphous SiO2 was synthesized using a co-precipitation combined H2 reduction method. The saturation magnetization of the (Fe70Co30)90/(SiO2)10 nanocomposite is as high as 200 emu/g, which is 4–5 times larger than that of traditional spinel ferrites. The frequency dependence of the complex initial permeability is intensely dependent upon the content of SiO2 insulating phase. With increasing the content of SiO2 to 10 wt.%, the cut-off frequency is drastically increased to over 1 GHz. The results show that a new high-frequency soft magnetic material with high saturation magnetization (M s) can be achieved by introducing FeCo/SiO2 nanocomposite.
Keywords: FeCo–SiO2; Magnetic materials; Nanocomposites; Permeability;

Crystallization kinetics and high-resolution X-ray diffraction analysis on nonlinear optical l-threonine single crystals by G. Ramesh Kumar; S. Gokul Raj; Thenneti Raghavalu; V. Mathivanan; M. Kovendhan; G. Bhagavannarayana; R. Mohan (4932-4936).
Crystallization parameters such as critical radius, critical free energy and volume free energy change have been evaluated for l-threonine single crystals using homogeneous nucleation theory. Metastable zone width and induction period measurements have been carried out experimentally. Interfacial energy values for the aqueous solution of l-threonine were also calculated from the solubility data. Optimization of growth parameters has been tried for bulk crystal growth and it has been discussed in detail. The crystalline quality of the bulk samples grown at different pH values have been tested by high-resolution X-ray diffraction analysis.
Keywords: Nucleation kinetics; Nonlinear optical materials;

Size-controllable synthesis of calcium carbonate nanoparticles using aqueous foam films as templates by Feng Guo; Ying Li; Hong-Xia Xu; Guo-Qing Zhao; Xiu-Juan He (4937-4939).
A new method for the synthesis of calcium carbonate nanoparticles using two types of foam which are separately stabilized by surfactants with opposite change has been described here. In detail, one type of foam is formed by the aqueous solution of CaCl2 which contains the anionic surfactant alkyl polyoxyethylene alcohol sulfate sodium (AES) and the other is formed by the aqueous solution of Na2CO3 and the cationic surfactant alkyl polyoxyethylene quaternary ammonium chloride (AEAC). Two types of foam contact each other in a specially designed apparatus after draining completely, then Ca2+ and CO3 2− entrapped by the surfactant layers at the thin borders between the foam bubbles react and result in the generation of CaCO3 nanoparticles. TEM determination showed that perfect mono-dispersed spherical nanoparticles were obtained and the size of particles can be conveniently controlled by changing the concentration of CaCl2 and Na2CO3. Also, the mechanism leading to the synthesis of CaCO3 nanoparticles was discussed in detail.
Keywords: Nanoparticles; Foam film; Surfactant;

Synthesis of binary and triple carbon nanotubes over Ni/Cu/Al2O3 catalyst by chemical vapor deposition by Chunnian He; Naiqin Zhao; Chunsheng Shi; Xiwen Du; Jiajun Li (4940-4943).
Novel binary and triple carbon nanotubes (CNTs) with one common catalytic particle encapsulated have been synthesized using Ni/Cu/Al2O3 catalyst, which was produced by a sol–gel method. But when using Ni/Al2O3 as catalyst, a mass of common CNTs, that is, one CNT with one catalytic particle encapsulated, was obtained. The results showed that copper-element doping to the Ni/Al2O3 catalyst played a key role in the synthesis of CNTs, signifying a novel approach to modify the Ni/Al2O3 catalyst. Based on the transmission electron microscopy observations, a simple growth mechanism was developed to describe the growth of the binary or triple CNTs, which could be well explained by a diffusion segregation process.
Keywords: Chemical vapor deposition; Carbon nanotubes; Electron microscopy;

We report the synthesis of CdS nanorods by reacting CdCl2 nanorods with H2S at room temperature. The preparation method was based on CdCl2 nanorods employed as chemical template. The length and the diameter of the obtained CdS nanorods are about tens micron and 120−300 nm, respectively. The phase and the crystallographic structure of the products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The composition of the products was investigated by X-ray photoelectron spectroscopy (XPS).
Keywords: Nanomaterials; Crystal growth;

Preparation of polyaniline-Al2O3 composites nanofibers with controllable conductivity by Geik Ling Teoh; Kong Yong Liew; Wan A.K. Mahmood (4947-4949).
Conducting polyaniline-Al2O3 composite nanofibers with varying conductivity was prepared by seeding with Al2O3 nanofibers and oxidative polymerization of aniline. TEM and FESEM demonstrated clearly the nanofibers of PANI-Al2O3 with average diameters of mean diameters of 37–52 nm and lengths of up to μm. The XRD diffractograms indicated that the nanocomposite has the emeraldine structure. The DSC and the FTIR studies showed that the nanocomposite was formed from interaction between the polymer and the Al2O3. The conductivity of the composite decreased with an increase in the Al2O3 content incorporated.
Keywords: Polyaniline; Alumina; Nanocomposites; Nanofibers;

The nonlinear electrical properties and accelerated aging behavior of the varistors, which are composed of ZnO–Pr6O11–CoO–Cr2O3–La2O3 (ZPCCL)-based ceramics, were investigated for different sintering temperatures. The increase of sintering temperature led to more densified ceramics, whereas it decreased the nonlinear properties and varistor voltage. The highest nonlinearity of varistors was obtained from sintering temperature of 1240 °C, in which the nonlinear coefficient is 79.4 and the leakage current is 0.3 μA. However, the highest stability of varistors was obtained from sintering temperature of 1260 °C, in which the %ΔV 1 mA is + 1.9%, the %Δα is − 10.6%, and the %ΔI L is + 20% for stress state of 95 V 1 mA/150 °C/24 h.
Keywords: Ceramics; Sintering; Electrical properties; Stability; Varistors;

Structural and optical properties of single-crystalline ultraviolet-emitting needle-shaped ZnO nanowires by Ahmad Umar; S.H. Kim; J.H. Kim; Y.K. Park; Y.B. Hahn (4954-4958).
Well-crystallized with excellent optical properties, needle-shaped ZnO nanowires have been synthesized on silicon substrate in a high density via the thermal evaporation of metallic zinc powder without the use of catalysts or additives. Extensive structural analysis showed that the grown nanowires are highly crystalline with the wurtzite hexagonal phase, grown along the [0001] in the c-axis direction. The presence of an optical-phonon E 2 mode in Raman spectrum at 437 cm− 1 and sharp and strong UV emission at 379 nm with no green emission in the room-temperature photoluminescence (PL) spectrum confirms good crystallinity with the excellent optical properties for the deposited nanowires.
Keywords: 68.65.+g; 78.66.Hf; 81.05.Dz; 81.10.Bk; Nanowires; High resolution transmission electron microscopy and SAED patterns; Optical characterization; ZnO; Semiconducting II–VI materials;

Self-assembled microspheres of glucose-containing polyaniline by alkali-guided method by E. Jin; Xing Wang; Na Liu; Wanjin Zhang (4959-4962).
Glucose-containing polyaniline (PANI) microspheres were prepared via a self-assembly process which started in alkaline solution by the oxidative polymerization of N-glucosylaniline (G-An). The products were characterized by SEM, TEM, FT-IR, UV–Vis, 1H NMR and GPC measurements. It was found that the polymerization of G-An by alkali-guided method gave complicated structures and both the pH value and the dose of oxidant could affect the morphology of the product.
Keywords: Polymer; Microstructure; Glucose-containing; Polyaniline;

Phase transformation in Cu–Cr–Zr–Mg alloy by Juanhua Su; Ping Liu; Hejun Li; Fengzhang Ren; Qiming Dong (4963-4966).
After solid solution treatment, the effects of aging processes on the microstructure and electrical conductivity of Cu–Cr–Zr–Mg lead frame alloy were investigated in order to determine the phase transformation and the time–temperature-transformation (TTT) behavior. The results show that aged at 470 °C the fine precipitation of an ordered CrCu2(Zr,Mg) phase is found in copper matrix as well as fine Cr and Cu4Zr, aged at 550 °C the phase CrCu2(Zr,Mg) is decomposed into Cu4Zr and Cr phase, aged at 600 °C the precipitates is bcc Cr only. The phase transformation kinetics equation was deduced from the Avrami empirical formula based on the linear relationship between the electrical conductivity and the volume fraction of the phase transformation.
Keywords: Cu–Cr–Zr–Mg alloy; Phase transformation; Conductivity; TTT curves;

Nanostructured tin dioxide (SnO2) is synthesized in the form of colloidal sol. Aniline monomer is polymerized in colloidal sol of SnO2 to prepare inorganic–organic hybrid nanocomposites. Optical band gap increases from 3.74 eV to 4.23 eV with increase of polyaniline concentration. The observed nonlinear current–voltage characteristics are satisfactorily explained using the Schottky type barriers. The temperature dependence of conductivity reveals three dimensional Mott's hopping process.
Keywords: Inorganic–organic; Nanocomposite; Optical; Electrical;