Materials Chemistry & Physics (v.90, #1)

Recent research developments in SnO2-based varistors by M.R. Cássia-Santos; V.C. Sousa; M.M. Oliveira; F.R. Sensato; W.K. Bacelar; J.W. Gomes; E. Longo; E.R. Leite; J.A. Varela (1-9).
This paper discusses some advances in research conducted on SnO2-based electroceramics. The addition of different dopants, as well as several thermal treatments in oxidizing and inert atmospheres, were found to influence the microstructure and electrical properties of SnO2-based varistor ceramics. Measurements taken by impedance spectroscopy revealed variations in the height and width of the potential barrier resulting from the atmosphere in which thermal treatments were performed. High nonlinear coefficient values, which are characteristic of high-voltage and commercial ZnO varistors, were obtained for these SnO2-based systems. All the systems developed here have potentially promising varistor applications.
Keywords: Varistors; SnO2; Nonlinear systems; Schottky barrier;

Crystallization and characterization of l-histidinium perchlorate single crystal by Reena Ittyachan; S.Xavier Jesu Raja; S.A. Rajasekar; P. Sagayaraj (10-15).
Single crystals of l-histidinium perchlorate (LHPC), a semiorganic nonlinear optical material have been successfully grown from aqueous solution, by slow evaporation solution growth technique. Single crystals in size 5 × 4 × 1 mm3 were grown in a period of 2 weeks. Single crystal XRD analysis confirmed that the grown crystals are pure form of LHPC. Faces of the crystal were indexed. The mechanical properties of the grown crystal have been studied using Vicker's microhardness tester. Microstructural imperfections of the as grown crystal have been studied. Photoconductivity studies were carried out using Keithley 485 picoammeter.
Keywords: Crystal growth; Morphology; Hardness; l-histidinium perchlorate, NLO test;

Synthesis and characterization of steam-stable AlMCM-41 by Kegong Fang; Jie Ren; Yuhan Sun (16-21).
Steam-stable and hexagonally ordered mesoporous aluminosilicate (MCM-41(h)) has been prepared via neutral-cationic route using butylamine and cetyltrimethylammonium bromide as co-templating agents. The mesostructure of the synthesized material could retain its integrity after exposure to 20% (v/v) water vapor in Ar at 1073 K for 4 h. It was believed that the steam stability might be related to the thicker framework walls, the higher condensation of surface silanol groups and the presence of some arrangements of zeolite five-ring subunits in the framework walls. In catalytic cracking of 1,3,5-triisopropylbenzene, the MCM-41(h) showed relatively stable activity under equivalent steaming conditions in comparison with the conventional AlMCM-41 material.
Keywords: Mesoporous aluminosilicate; Steam-stable; Characterization;

The Ti-doped ZnO (ZnO:Ti) films were prepared by simultaneous radio frequency (rf) magnetron sputtering of ZnO and dc magnetron sputtering of Ti. The Ti oxides increased with the decrease in substrate temperature. Therefore, by decreasing the substrate temperature, X-ray peaks shifted towards a lower diffraction angle. When the substrate temperature increased from 50 to 150 °C, the crystallinity increased obviously, but it decreased slightly at 200 °C. The morphologies of films were significantly affected by the substrate temperature. The electrons of ZnO:Ti films may be originated from the oxygen vacancies and Ti donors. The mean free path of carriers were much shorter, therefore grain boundary scattering could be ruled out. The variation in mobility could be due to the ionized impurity scattering and surface roughness. The resistivity of ZnO:Ti film at 100 °C has a minimum of 9.69 × 10−3  Ω cm, which is mainly due to the higher product of carrier concentration and mobility. At various substrate temperatures, the visible transmission of ZnO:Ti films was high.
Keywords: Substrate temperature; Morphologies; Resistivity; Transmission;

Si3N4–MgO–Y2O3 ceramic materials have been fabricated by pressureless sintering, which overcomes the limitations of hot pressing. The amount of Y2O3 has a strong influence on the densification behavior and mechanical properties of the sintered materials. The pressureless sintered silicon nitride with 5 wt.% MgO + 4 wt.% Y2O3 achieved a relative density of 99%, a bending strength of 950 MPa and a fracture toughness of 7.5 MPa m−1/2.
Keywords: Silicon nitride; Sintering;

The three-dimensional confinement effects in chemically deposited ZnSe quantum dots in thin film form are experimentally detected and analyzed. Experimentally measured band gap shifts with respect to the bulk value for quantum dot thin films with various average nanocrystal sizes are compared with the predictions of the effective mass approximation model (i.e., Brus model), the hyperbolic band model, as well as of the Nosaka's approach. It is found that the original Brus model fails to predict correctly the ΔE g(R) dependence, the deviations from experimental data being largest for the smallest nanocrystals. However, using the Brus equations with a single modified parameter—the relative dielectric constant of the material (setting it to approximately four times smaller value than in the case of the bulk material), leads to an excellent agreement with the experimental observations. This seems to be in line with some existing indications that the nanocrystal ɛ r values should be smaller than the corresponding values for bulk specimen, due to the inability of the lattice polarization to follow the more rapid electron and hole motions associated with a smaller crystal radius. On the other hand, application of the hyperbolic band model leads to only a moderate improvement of the agreement with the experimental data in comparison to the Brus model, implying that the electron and hole band non-parabolicity is of minor importance in the case of the studied nanocrystalline material. The possibility of an electron leakage outside the nanoparticle seems to be another effect of key importance for the presently studied system, besides the reduction of ɛ r value upon crystal size decrease. This conclusion is drawn on the basis of excellent agreement of the predicted ΔE g(R) dependence according to Nosaka's approach with our experimental data for chemically deposited ZnSe quantum dots in thin film form.
Keywords: Zinc selenide; Thin films; Quantum dots; Quantum size effects; Quantum confinement effects; Band gap energy;

A composite multilayer film constructed of Dawson anion [P2Mo18O62]6− and diazo resin (DR) was prepared by the electrostatic layer-by-layer (LbL) self-assembly method. The film could be stabilized by the photoinduced interaction between Dawson anion and diazo resin. IR spectra and X-ray photoelectron spectra revealed the possible occurrence of partial transformation from electrostatic interaction to covalent interaction between layers of the film after irradiation by UV light. Such transformation evidently increases the endurance of the film, which was demonstrated by AFM images and etching experiments with organic solvent. This study provides a new route to stabilze the polyoxometalate-based multilayer film by virtue of the photoinduced reaction with photosensitive polymer.
Keywords: Multilayers film; Polyoxometalate; Photoinduced interaction;

Atomic force microscopy (AFM) has been used to investigate the growth mechanisms of the l-arginine phosphate monohydrate (LAP) crystal grown from the aqueous solution containing excessive amount of l-arginine molecules. Under this condition, the LAP crystals grow by both 2D nucleation mechanism and spiral dislocation mechanism. 2D nucleation growth is the intrinsical growth mechanism owing to the crystal structure of LAP. The spiral growth mechanism probably results from the distortion of the crystal lattices produced by the LA n P unit or separated l-arginine molecule. Pinning points of impurities and curved step type induced by them are also explored.
Keywords: Atomic force microscopy; Crystal growth mechanism; Two-dimensional nuclei; Dislocation; Nonlinear optical (NLO) material;

Facile in situ synthesis of oriented LiNbO3 single crystals in a polymer matrix by Michael W. Pitcher; Yanan He; Patricia A. Bianconi (57-61).
Nanocrystals of stoichiometry LiNbO3 are produced in a film of poly(4-vinylpyridine) (4-PVP) in a matrix-mediated in situ sol–gel-like synthesis. These crystals are produced at room temperature, and show identical size, morphology, phase, and crystallographic orientation. These features are produced by the application of aspects of biological mineralization to the fabrication of this non-biological composite.
Keywords: Sol–gel; Biomineralization; LiNb(OEt)6;

Luminescence characteristics of europium-ion doped BaMgAl10O17 phosphors prepared via a sol–gel route employing polymerizing agents by Chung-Hsin Lu; Wei-Tse Hsu; Chien-Hao Huang; S.V. Godbole; Bing-Ming Cheng (62-68).
Europium-ion doped BaMgAl10O17 phosphors were prepared via both a sol–gel route and the conventional solid-state route. The effects of various preparation conditions on the optical properties of BaMgAl10O17 based phosphors were investigated. The position of charge transfer band and emission characteristics of europium ions in Ba0.9Eu0.1MgAl10O17 are observed to be different between those prepared by the sol–gel route and those derived from the solid-state route. The sites occupied by europium ions in BaMgAl10O17 are found to depend upon the method of synthesis. The ratios of the intensity of 610 nm emission (5D07F2) to that of 590 nm emission (5D07F1) suggest that Eu3+ ions are located in a more asymmetric environment for the sol–gel-derived phosphors as compared to that in phosphors prepared via the solid-state route. VUV-excited emission characteristics indicate that the prepared phosphors generate intense emission at 458 nm under excitation at 147 nm. In addition, the luminescence intensity of the sol–gel-derived phosphors is greater than that of the solid-state-route-derived phosphors. The sol–gel method employing polymerizing agents is demonstrated to be suitable for the synthesis of phosphors used in plasma display panels.
Keywords: Sol–gel; Phosphor; Luminescence; Barium magnesium aluminate;

Highly ordered Ag nanowire arrays with high aspect ratio and highly dense self-supporting Ag nanowire patterns were successfully prepared using cyclic voltammetry with the assistance of anodic aluminum oxide (AAO) template from AgNO3 aqueous solution without any additives. The diameter of the Ag nanowire in the arrays is about 60 nm and the length can be tuned from 30 to 1 μm or even shorter with the aspect ratio from 500 to 5.
Keywords: Silver; Nanowire arrays; Cyclic voltammetry; AAO template;

Fabrication of transition metal sulfides nanocrystallites via an ethylenediamine-assisted route by Qingsheng Wang; Zhude Xu; Haoyong Yin; Qiulin Nie (73-77).
Many binary transition metal sulfides nanocrystallites MS (M = Zn, Cd, Co, Ni) with different morphologies have been successfully prepared in an ethylenediamine solution of metal salts and (NH4)2S (or thiourea) using a facile hydrothermal method. The products are characterized by powder X-ray electron diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the selected area electron diffraction (SAED), respectively. UV–visible optical absorption spectra clearly indicate the presence of quantum size effects in some transition metal sulfides nanocrystallites and the possible mechanism of ethylenediamine-assisted is also briefly discussed. This method may also be extended to controllable synthesis of other metal chalcogenides with different morphologies, such as nanowires, nanorods, and nanodisks, etc.
Keywords: Chalcogenides; Nanostructures; Chemical synthesis; Electron microscopy; Microstructure;

Three Er3+-doped tellurite glasses with compositions of 70TeO2–30ZnO, 70TeO2–20ZnO–10Nb2O5 and 70TeO2–20ZnO–5BaO–5Nb2O5 have been investigated for developing fiber and planar broadband amplifiers and lasers. The optical spectroscopic properties and thermal stability of Er3+-doped tellurite glasses have been discussed. The results show that the incorporation of Nb2O5 increases the thermal stability of Er3+-doped tellurite glasses significantly, Er3+-doped niobium tellurite glasses 70TeO2–20ZnO–10Nb2O5 and 70TeO2–20ZnO–5BaO–5Nb2O5 exhibit the good thermal stability (ΔT  > 150 °C), the large emission cross-section (>10 × 10−21  cm2) and broad full width at half maximum (∼65 nm), will be preferable for broadband Er3+-doped fiber amplifiers.
Keywords: Glasses; Annealing; Differential scanning calorimetry; Photoluminescence spectroscopy; Luminescence;

Glasses with compositions 20MO·xBi2O3·(80−x)B2O3 (M = Ba, Sr) with 10 ≤  x  ≤ 60 (in mol%) have been prepared using the normal melt-quench technique. The optical absorption spectra of the glasses have been recorded in the wavelength range 400–700 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed and indirect forbidden transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi2O3 in these glasses is acting partly as network modifier and partly as network former. Values of the direct-current electrical conductivity have been measured from 373 to 623 K and the activation energy has been calculated. The variations in optical band gap, density and electrical conductivity with Bi2O3 content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity are also reported.
Keywords: Oxide glasses; Optical properties; Density; Indirect semiconductor; Electrical conductivity;

Study of thick-coated spherical polymer brushes grown from a silicon gel surface by atom transfer radical polymerization by Hongtu Li; Hongwen Zhang; Yaxin Xu; Kai Zhang; Peng Ai; Xu Jin; Jingyuan Wang (90-94).
A series of thick-coated homopolymer and block polymer brushes on spherical silicon gel have been successfully studied by combining initiator and atom transfer radical polymerization (ATRP). The silicon gel initiator was prepared by self-assemble. The homopolymer brushes of poly (methyl methacrylate) (PMMA), poly (acrylamide) (PAAM) and their diblock copolymer (PMMA/PAAM) were prepared by ATRP on the surface of a modified spherical silicon gel. The structure of the polymer was characterized by Fourier-transformed infrared and X-ray photoelectron spectroscopy (XPS). The results revealed that the first polymer layer of the surface was partly covered with the second polymer layer after block copolymerized with the second monomer. The surface morphology of the particles revealed that the particles were composed of an organic shell and an inorganic core. The organic content on the silicon gel was high.
Keywords: ATRP; Polymer brushes; Graft density; Thick-coated;

FePt/C granular thin films for high-density magnetic recording by Xiao-Hong Xu; Hai-Shun Wu; Xiao-Li Li; Fang Wang (95-98).
The formation of L10 FePt nanoparticles by annealing of FePt/C multilayer films was studied. After annealing at 550 °C for 30 min, the superlattice peaks (0 0 1) and (1 1 0) found in the X-ray diffraction pattern of the FePt/C films indicate that the face-centered cubic disordered phase has been partially transformed into the L10 phase. FePt/C thin films became magnetically hard with a coercivity in the range 1.8–9.2 kOe due to the high anisotropy energy associated with the L10 ordered phase. The coercivity of the films decreased rapidly with increasing C layer thickness. With increasing C content, the grain size and intergrain interaction of the FePt/C multilayer films decreased. The coercivity not only depends on the C content, but also on the structure of the FePt/C mutilayer. The [FePt 3 nm/C 3 nm]10 sample shows a small dipolar interaction.
Keywords: FePt/C thin films; Coercivity; Multilayers; Intergrain interaction;

The synthesis of heterogeneous phosphine-free palladium-based catalyst materials was accomplished in a straightforward, two-step reaction using solid phase extraction. This involves functionalization of solid inorganic sorbents such as aluminium oxide, silica gel and titanium dioxide with organic chelate, i.e. dimethyl glyoxime (DMG). The above functionalized materials were transformed into palladium ion-sorbed DMG-functionalized materials by solid phase extraction. The synthesized materials were characterized by a variety of experimental techniques. One of the best-synthesized materials was used for the catalytic evaluation using the Heck reaction. Highly crystalline materials with a controlled size, porosity and uniform distribution of the palladium ion were prepared by this method.
Keywords: Chelate-functionalized inorganic sorbents; Heterogeneous catalyst; Palladium; Solid phase extraction;

Zinc sulfide thin films were prepared by chemical bath deposition from different host solutions. The variation in the optical and electrical properties of these films with the pH value of the reaction mixture was investigated in detail. The films showed a high transmission (>80%) and a wide band gap of 3.93 eV. The resistivity of the films was found to decrease with the increase in pH of the reaction mixture and was ≈104  Ω cm for pH 10.6. The refractive index, extinction coefficient and the dielectric constants of the chemical-bath-deposited ZnS films were measured. The films prepared from the zinc nitrate solution have been found to possess a higher band gap, better transparency and surface morphology compared to the films grown from zinc chloride solution.
Keywords: ZnS films; Chemical bath deposition; Thin films;

Synthesis and piezoelectric and ferroelectric properties of (Na0.5Bi0.5)1−x Ba x TiO3 ceramics by Qing Xu; Shutao Chen; Wen Chen; Sujuan Wu; Jing Zhou; Huajun Sun; Yueming Li (111-115).
(Na0.5Bi0.5)1−x Ba x TiO3 powders were synthesized by a citrate method, and the piezoelectric and ferroelectric properties of the ceramics were investigated. The results indicate that the citrate method is an advantageous alternative route to the conventional method in producing (Na0.5Bi0.5)1−x Ba x TiO3 ceramics. Homogeneous and fine powders with a pure perovskite structure were derived from precursor solutions with a mole ratio of citric acid to total metal cation content (C/M) of 1.25 by calcining at 600 °C for 1 h. The ceramics made by the citrate method exhibit superior piezoelectric properties near the rhombohedral–tetragonal morphotropic phase boundary. The piezoelectric constant (d 33) and electromechanical coupling factor (k p) attain maximum values of d 33  = 180 pC N−1 and k p  = 0.28 at x  = 0.06, corresponding to a relatively large remanent polarization of P r  = 37.1 μC cm−2 and a relatively low coercive field of E c  = 42.7 kV cm−1.
Keywords: Ceramics; Chemical synthesis; Piezoelectricity; Ferroelectricity;

Template removal from polycrystalline silicalite-1 self-supporting layer by Ivan Jirka; Arlette Zikánová; Pavel Novák; Milan Kočiřík; Jan Weber; Hana Pelouchová; Marian Čerňanský (116-122).
The extent of thermal template (tetra-propyl-ammonium: TPA+) removal from a silicalite-1 layer by heating in air was investigated. While a temperature of 330 °C was sufficient to eliminate all N-containing template species from the surface region of the layer (i.e., within a depth of ≈10 nm), their complete elimination from the bulk even at 550 °C was not achieved. This was caused by a series of reactions proceeding at high temperatures, involving the products of TPA+ thermal degradation. A substantial amount of C-containing template species remained in the sample even after a thermal treatment at 550 °C. A role the SiO2 phase of low organization present in the silicalite-1 layer plays in the retention of the products of thermal degradation has been proposed. Additionally, the stability of TPA+ irradiated by microwaves was examined. Only minor morphological changes of the layer upon thermal template removal were revealed by atomic force microscopy.
Keywords: Microporous materials; Surface properties; X-ray photoelectron spectroscopy; Atomic force microscopy; Silicalite-1;

An aqueous sol–gel route to synthesize nanosized lanthana-doped titania having an increased anatase phase stability for photocatalytic application by K.V. Baiju; C.P. Sibu; K. Rajesh; P. Krishna Pillai; P. Mukundan; K.G.K. Warrier; W. Wunderlich (123-127).
A novel synthesis method is reported, involving peptisation and doping of lanthana on colloidal sol–gel titania derived from titanyl sulphate, where the anatase phase has a high stability above 800 °C and a specific surface area of 101 m2  g−1 for the gel calcined at 500 °C. The undoped gel calcined at 600 °C has an average crystallite size of 12 nm, but under identical experimental conditions, the doped one shows an average crystallite size of 7 nm. The doped titanium oxide has a specific surface area of 25 m2  g−1 even after calcination at 800 °C. The exceptionally high phase stability and surface area are due to the specific synthesis method. Doped titania also shows an excellent photoactivity as evaluated by the extent of decomposition of methylene blue when exposed to ultraviolet light.
Keywords: Sol–gel; Titanyl sulphate; Photocatalyst; Anatase; Rutile;

Effect of discharge pulsating on microarc oxidation coatings formed on Ti6Al4V alloy by Y.M. Wang; D.C. Jia; L.X. Guo; T.Q. Lei; B.L. Jiang (128-133).
Ceramic coatings were formed on a Ti6Al4V alloy in a Na2SiO3–KOH–(NaPO3)6 aqueous solution, using the pulsating microarc oxidation method. A constant voltage (500 V) was applied to reveal the effect of the positive-pulse duty cycle on the growth rate, microstructure and phase composition of the coating. To obtain the optimum process, a constant current density (60 mA cm−2) combined with a stepped adjusting of the positive-pulse duty cycle was also proposed. The coatings are mainly composed of anatase and rutile (TiO2). As the duty cycle increases, rutile increases and becomes the predominant phase. The coating formed at a duty cycle of 8% indicates an optimum combination of structure and thickness. When applying a constant current density, the growth rate of coatings is significantly increased compared with the application of a constant voltage. Further, using the stepped adjusting of the duty cycle, the microstructure of the coatings is improved obviously.
Keywords: Ti–Al–V alloy; Coatings; Microarc oxidation; Discharge pulsating; Microstructure;

Raman scattering from deuterated potassium dihydrogen phosphate crystals by W.L. Liu; H.R. Xia; X.Q. Wang; H. Han; G.W. Lu (134-138).
The normal vibration modes of deuterated potassium dihydrogen phosphate (DKDP) crystals were analyzed basing on the space group theory. The lattice vibration spectra of DKDP, which arise mainly from internal vibrations of P–O tetrahedrons, were recorded by a micro-Raman spectrophotometer system. The four characteristic internal vibration modes of the D2PO4 anion in KD2PO4 are assigned as 880 cm−1 ( υ 1 , asymmetrical P(OD)2 stretching vibration), 356 cm−1 ( υ 2 , in-plane P(OD)2 bending vibration), 512/540 cm−1 ( υ 3 , PO2 bending vibration) and 967 cm−1 ( υ 4 , in-plane PO2 symmetrical stretching vibration). Excellent agreement has been obtained between the theoretical studies and experimental investigations.
Keywords: Optical materials; Raman spectroscopy and scattering; Crystal structure;

A new multi-branched two-photon photopolymerization initiator: synthesis and non-linear optical properties of a 1,3,5-triazine-based octupolar molecule by Yunxing Yan; Xutang Tao; Yuanhong Sun; Guibao Xu; Chuankui Wang; Jiaxiang Yang; Xian Zhao; Yongzhong Wu; Yan Ren; Minhua Jiang (139-143).
A new multi-branched two-photon photopolymerization initiator, tris-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to TPVPA) has been synthesized and characterized. The experimental results confirmed that TPVPA is a good two-photon absorbing chromophore and operative two-photon photopolymerization initiator. The calculated two-photon absorption cross-section of TPVPA is 42.4 × 10−50  cm4  s photon−1. A microstructure using TPVPA as initiator has been fabricated under irradiation of a Ti:sapphire femtosecond laser at 830 nm. The possible photopolymerization mechanism is discussed.
Keywords: Octupolar molecule; Two-photon absorption; Non-linear optical properties; Two-photon photopolymerization;

l-Histidine tetrafluoroborate (l-HFB) is a highly transparent monoclinic crystal with favourable properties of efficient frequency conversion. Single crystals have been grown successfully by a slow evaporation method. The solubility of the l-HFB crystal is very high in water when compared to other solvents like acetone or methanol. In this study, l-HFB crystals were grown from aqueous solution. The grown crystals have been subjected to X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), second harmonic generation and ultraviolet–visible spectral analyses. Thermogravimetric and differential scanning calorimetry analyses have been performed to study the thermal stability of the crystal. Capacitance and dielectric loss measurements were carried out and the dielectric constant was calculated at room temperature in the frequency range 1 kHz–40 MHz. The dielectric constant at room temperature remains constant for the entire frequency range.
Keywords: Optical materials; Crystal growth; X-ray diffraction; Dielectric properties; Single crystals; l-Histidine tetrafluoroborate;

Soft growth of the ZnSe compound from alkaline selenosulfite solutions by T. Kosanovic; M. Bouroushian; N. Spyrellis (148-154).
The electrodeposition of ZnSe from alkaline selenosulfite, (SeSO3)2−, baths of a zinc ion complex has been studied both in an experimental and a mechanistic interpretation manner. The effect of various process parameters (bath composition, substrate nature and rotation, temperature, deposition time) on the structural and morphological properties of the deposits was investigated. The structure-related results were valuated by means of X-ray diffraction and scanning electron microscopy (SEM). A large amount of experimental data issued by applying multiple variants of the presently described method showed that the production of a stoichiometric, though amorphous in structure, ZnSe compound is possible.
Keywords: ZnSe; Thin films; Crystal growth; Selenosulfite solution; Powder diffraction;

Luminescent and photocatalytic properties of cadmium sulfide nanoparticles synthesized via microwave irradiation by Huaming Yang; Chenghuan Huang; Xianwei Li; Rongrong Shi; Ke Zhang (155-158).
Uniform cadmium sulfide (CdS) nanoparticles of about 6 nm in crystal size have been successfully synthesized via microwave irradiation. The as-prepared sample has a uniform morphology and high purity. The red photoluminescence spectrum of the CdS nanoparticles displays a strong peak at 602 nm by using a 300 nm excitation wavelength. The photocatalytic oxidation of methyl orange (MeO) in CdS suspensions under ultraviolet illumination was investigated. The results indicate that a low pH value (pH 2.0) and low reaction temperatures (20–30 °C) will facilitate the decolorization of the MeO solution. The photodegradation degree decreases with increasing the pH value and temperature of solution. The efficiency of the recycled CdS semiconductor becomes lower due to the deposit of elemental Cd on the CdS surface, which weakens the photocatalytic activity. The luminescent and photocatalytic mechanisms of the as-prepared CdS nanoparticles were primarily discussed. Microwave irradiation is proved to be a convenient, efficient and environmental-friendly one-step route to synthesize nanoparticles.
Keywords: CdS nanoparticles; Microwave irradiation; Luminescence; Photocatalysis; Decolorization;

A computational analysis of ordering in fluoro-smectogen, 4-propoyloxyphenyl 4-(4-trifluoromethylbenzoyloxy) benzoate (FLUORO), has been carried out with respect to translatory and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment at each atomic centre. The modified Rayleigh–Schrödinger perturbation theory with the multi-centered-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for short-range interactions. The interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium (i.e., non-interacting and non-mesogenic solvent, benzene) at room temperature (300 K), transition temperature (488 K) and above transition temperature (550 K). The flexibility of various configurations has been studied in terms of the variation of probability due to small departures from the most probable configuration. An attempt has been made to develop a new and interesting model of smectogen in a dielectric medium. The present investigation provides theoretical support to the experimental observations.
Keywords: Liquid crystals; Computer modelling and simulation; Fluoro-smectogen;

In order to study the effect of molybdenum ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted by molybdenum ions in the fluence range 1 × 1016 to 5 × 1017  ions cm–2 at maximum 160 °C, and at an extracted voltage of 40 kV. The valence of the surface layer was analyzed by X-ray photoemission spectroscopy. Three-sweep potentiodynamic polarization measurements were employed to value the aqueous corrosion resistance of zirconium in a 1N H2SO4 solution. Scanning electron microscopy (SEM) was performed for the three-sweep potentiodynamic polarized samples. It was found that the aqueous corrosion resistance of zirconium implanted with molybdenum declined with raising fluence. The greater is the implantation fluence, the bigger is the decline. And the natural corrosion potential of the implanted zirconium became more positive than that of the as-received zirconium. Finally, the mechanism of the corrosion resistance decline of the molybdenum-implanted zirconium is discussed.
Keywords: Zirconium; Corrosion resistance; Molybdenum ion implantation; Potentiodynamic polarization; Immersion test;

Mechanosynthesis and process characterization of nanostructured manganese ferrite by F. Padella; C. Alvani; A. La Barbera; G. Ennas; R. Liberatore; F. Varsano (172-177).
Nanocrystalline MnFe2O4 particles were synthesized by a high-energy ball milling technique, starting from a manganosite (MnO) and hematite (α-Fe2O3) stoichiometric powder mixture. The mechanosynthesis process was performed at room temperature both in hardened steel and in tungsten carbide vials. X-ray powder diffraction quantitative phase analysis by the Rietveld method was used to study the chemical transformations promoted by the milling action. The nanocrystalline MnFe2O4 spinel phase begins to appear after 10 h of milling and reaches its maximum content (≈0.8 molar fraction) after 35 h of milling. A prolonged milling time induces a dramatic contamination of the powder mixture, when hardened stainless steel was adopted, due to metallic iron originating from vial and balls debris. Ball milling is able to induce a redox reaction between FeIII and metallic iron, transforming the MnFe2O4 spinel phase into a wüstite type (Fe, Mn)O phase. The yield of the hydrogen production reaction on synthetised materials is reported.
Keywords: Manganese ferrite; Mechanosynthesis; Nanostructured ferrite; Hydrogen production; Rietveld method;

The coated layers fabricated on the tool steel D2 by thermoreactive deposition/diffusion (TRD) and TRD + plasma nitriding have been investigated on the tribologic characteristics against the counter ring made of a hardened O2 steel. The test was conducted in a block-on-ring tribometer in dry wear condition in the air. The results showed that the chromium carbide, Cr7C3-dominated layer, provided by the TRD performed poor wear resistance even worse than that of the neutral hardened D2 steel because of tribochemical reaction and microploughing. However, the chromium nitride, CrN, layer derived from the post-treatment of plasma nitriding exhibited an outstanding wear resistance due to abrasion action.
Keywords: Thermoreactive deposition/diffusion; Plasma nitriding; Wear resistance;

PEEK composites reinforced by nano-sized SiO2 and Al2O3 particulates by M.C. Kuo; C.M. Tsai; J.C. Huang; M. Chen (185-195).
The poly(ether-ether-ketone) (PEEK) polymer filled with nano-sized silica or alumina measuring 15–30 nm to 2.5–10 wt.% are fabricated by vacuum hot press molding at 400 °C. The resulting nanocomposites with 5–7.5 wt.% SiO2 or Al2O3 nanoparticles exhibit the optimum improvement of hardness, elastic modulus, and tensile strength by 20–50%, with the sacrifice of tensile ductility. With no surface modification for the inorganic nanoparticles, the spatial distribution of the nanoparticles appears to be reasonably uniform. There seems no apparent chemical reaction or new phase formation between the nanoparticle and matrix interface. The crystallinity degree and thermal stability of the PEEK resin with the addition of nanoparticles are examined by X-ray diffraction, differential scanning calorimetry, and thermogravity analyzer, and it is found that a higher crystallinity fraction and degradation temperature would result in the composites as compared with the unfilled PEEK.
Keywords: Nanocomposites; PEEK; Mechanical properties; Thermal stability;

An ever first attempt to study the effects of cation substitution at the V sites of LiNiVO4, especially upon the electrochemical activity of the same has been made in the present investigation. A series of compounds with the general formula viz., LiNiM x V1−x O4 with M = Co, Mg and Al; x  = 0.0, 0.1, 0.3 and 0.5 has been synthesized by adopting a novel solution-based soft-chemical route namely the Starch-Assisted Combustion (SAC) method. Powder X-ray diffraction (PXRD) studies indicate the possible solubility limit of all the three selected cations viz., Co, Mg and Al with V in LiNiVO4 matrix to a level of 10% and the rest of the compositions are observed to contain mixed phases. FTIR vibrational spectroscopic studies also confirm the above observation. SEM, particle size distribution, cyclic voltammetric (CV) and electrochemical cycling studies have also been carried out for these compounds with a view to gain more knowledge about the impact of added metal cations towards partial substitution of vanadium in the chosen LiNiVO4 matrix. It is interesting to note that CV evidences high Li+ reversibility in the voltage region of 4–5 V for the three solid solutions with x  = 0.1. Based on the performance results of the electrochemical charge–discharge studies carried out on these compounds, only LiNiAl0.1V0.9O4 seems to have a better chance as suitable cathode material for rechargeable lithium battery applications.
Keywords: Cathode materials; LiNiM x V1−x O4; Lithium batteries;

The research on the surface photovoltaic properties of porphyrin affected by nano-TiO2 by Ziheng Li; Dejun Wang; Yingyan Shi; Ping Wang; Xingqiao Wang (203-206).
The degeneration of energy level of α, β, γ, δ-tetrahydroxylphenylporphyrin (THPP) and red shift of the photovoltage peaks of THPP are observed as the size of nano-TiO2 decreasing using surface photovoltage (SPV) technique, while that of α, β, γ, δ-tetraphenylporphyrin (TPP) have little change. The reason for that is the existence of hydroxyls of THPP, which interact with the surface of nano-TiO2. This difference was also demonstrated by IR spectrum.
Keywords: Nano-TiO2; Bonding; Quasi-metalloporphyrin;

The effect of O2 partial pressure on the structure and photocatalytic property of TiO2 films prepared by sputtering by Baoshun Liu; Xiujian Zhao; Qingnan Zhao; Chunling Li; Xin He (207-212).
The TiO2 films were prepared on slide substrates by dc reactive magnetron sputtering at different oxygen partial pressure, and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Fourier transform infrared spectrometry (FT-IR). The degradation of methyl orange aqueous solutions was used to evaluate the photocatalytic activity. The results show that all films show crystalline anatase structure irrespective of oxygen partial pressure. The surface oxygen element exists in three forms, the first one is TiO2, the second one is OH and the last one is physical absorbed water. The films deposited at oxygen partial pressure of 0.035 and 0.040 mTorr present better photocatalytic activity, which shows clear tendency to increase with oxygen partial pressure. Such photocatalytic activity results are considered to correlate with the crystalline structure, grain sizes and the OH concentration.
Keywords: Magnetron sputtering; Titanium dioxide; Oxygen partial pressure; Photocatalysis;