Thermal-dynamical properties and pressure dependence of phonon spectrum of ordered Si<Subscript>50</Subscript>Ge<Subscript>50</Subscript> alloy based on <Emphasis Type="Italic">ab initio</Emphasis> methods

The phonon spectrum of ordered zincblende Si₅₀Ge₅₀ alloy is calculated by ab initio method. The energy band structure at zero pressure and the pressure dependence of phonon dispersion curves are shown up to 20 GPa. The calculation finds a pressure-induced softening of the transverse acoustic phonon mode and the mode frequency reaching zero at about 14 GPa, which indicate breaking of the symmetry and formation of a new phase under high pressure. Supported by the National Natural Science Foundation of China (Grant No. 50771090), the State Key Program for Basic Research of China (Grant No. 2005CB724404) and the Program for Changjiang Scholars and Innovative Team (Grant No. IRT0650)     

Controlled synthesis and magnetic properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> walnut spherical particles and octahedral microcrystals

Magnetite Fe₃O₄ walnut spherical particles and octahedral microcrystals were successfully synthesized from K₄ [Fe (CN)₆], K₃ [Fe (CN)₆] and NaOH reagents via a simple hydrothermal process. And the uniform morphology of octahedral microcrystals was obtained in the presence of ethylene glycol. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the Fe₃O₄ walnut spherical particles and octahedral microcrystals were single crystals with the face-center cubic structure and with size distributions from 2.2 to 8.6 μm and 1.6 to 12.5 μm, respectively. Their magnetic properties were detected by a vibrating sample magnetometer at room temperature. The walnut spherical particles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) being 150.57 Oe, 97.634 and 12.05 emu/g, respectively. For the octahedral microcrystals they were 75.28 Oe, 101.90 and 6.69 emu/g, respectively. Different sizes of walnut spherical particles were controlled synthesized through adjusting the NaOH concentration. It was found that ethylene glycol molecules have a significant effect on the formation of Fe₃O₄ octahedra. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ products. Supported by Fund of weinan Teachers University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Co-precipitation/hydrothermal synthesis of BiFeO<Subscript>3</Subscript> powder

A coprecipitation/hydrothermal route was utilized to fabricate pure phase BiFeO3 powders using FeCl3·6H2O and Bi（NO3）3·5H2O as starting materials, ammonia as precipitant and NaOH as mineralizer. The synthesized powders were characterized by XRD, SEM and DSC-TG analysis. In the process, single-phase BiFeO3 powders could be obtained at a hydrothermal reaction temperature of 180 ℃, with NaOH of 0.15 mol/L, in contrast to 200 ℃ and 4 mol/L for conventional hydrothermal route. Meanwhile, the micro-morphology of synthesized BiFeO3 powders changed with different reaction temperatures and concentrations of NaOH. The N6el temperature, Curie temperature and decomposition temperature of the synthesized BiFeO3 powders were detected to be 301 ℃, 828 ℃ and 964 ℃, respectively. The hydrothermal reactions mechanism to fabricate BiFeO3 powders were discussed based on the in-situ transformation process.     

Synthesis ofNanocrystalline RuO2（60%）-SnO2（40%） Powders by Amorphous Citrate Route

Nanometer RuO2-SnO2 was synthesized by the citrate-gel method using RuCl3, SnCl4 as cation sources, citric acid as complexing agent and anhydrous ethanol as solvent. The structures of the derived powders were characterized by thermogravimetric and differential thermal analysis, X-ray diffraction, transmission electron microscope, and Brunauer-Emmett-Teller surface area measurement. The pure, fine and amorphous powders was obtained at 160℃. The materials calcined at above 400 ℃ were composed of rutile-type oxide phases having particle sizes of fairly narrow distribution and good thermal resistant properties. By adding SnO2 to RuO2, the Ru metallic phase can be effectively controlled under a traditional temperature of preparation for dimensional stable anode.     

Dielectric tunable properties of BaTi<Subscript>4</Subscript>O<Subscript>9</Subscript>-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> microwave composite ceramics

BaTi₄O₉-doped Ba_0.6Sr_0.4TiO₃ (BST) composite ceramics were prepared by the conventional solid-state reaction and their structure, dielectric nonlinear characteristics and microwave dielectric properties were investigated. The secondary phase of the orthorhombic structure Ba₄Ti₁₃O₃₀ is formed among BST composite ceramics with the increase of BaTi₄O₉. At the same time, a duplex or bimodal grains size distribution shows fine grains in a coarse grain matrix. The degree of frequency dispersion of dielectric permittivity below T _m is increased initially and then decreased with respect to BaTi₄O₉. As the BaTi₄O₉ content increases, the tunability of composite ceramics decreases, while the Q value increases. Interestingly, 70 wt% BaTi₄O₉-doped BST has a tunability ∼4.0% (under 30 kV/cm biasing) versus a permittivity ∼68 and quality factor ∼134.1 (at ∼3.2 GHz). Supported by the Ministry of Science and Technology of China through 973-project (Grant No. 2009CB623302), the Cultivation Fund of the Key Scientific and Technical Innovation Project, Ministry of Education of China (Grant No.707024), Shanghai Committee of Science and Technology (Grant No. 07DZ22302), and Shanghai Foundation Project under 06JC14070     

Formation of bulk ferromagnetic nanostructured Fe<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>14</Subscript>B<Subscript>6</Subscript> alloys by metastable liquid spinodal decomposition

Nanostructured Fe₄₀Ni₄₀P₁₄B₆ alloy ingots of 3–5 mm in diameter could be synthesized by a metastable liquid state spinodal decomposition method. For undercooling ΔT > 260 K, the microstructure of the undercooled specimen had exhibited liquid state spinodal decomposition in the undercooled liquid state. The microstructure could be described as two intertwining networks with small grains dispersed in them. For undercooling ΔT > 290 K, the overall microstructure of the specimen changed into a granular morphology. The average grain sizes of the small and large grains are ≅ 30 nm and ≅ 80 nm, respectively. These prepared samples are soft magnets with saturation magnetization B _s ≅ 0.744 T. Supported by the Hong Kong Research Grants Council the National Natural Science Foundation of China (Grant No. 50861007) and Xinjiang University Doctoral Research Start-up Grant (Grant No. BS050102)     

Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by sulfurizing different multilayer metal precursors

Cu₂ZnSnS₄ (CZTS) thin films were successfully fabricated on glass substrates by sulfurizing Cu-Sn-Zn multilayer precursors, which were deposited by ion beam sputtering and RF magnetron sputtering, respectively. The structural, electrical and optical properties of the prepared films under various processing conditions were investigated in detail. Results showed that the as-deposited CZTS thin films with the precursors by both ion beam sputtering and RF magnetron sputtering have a composition near stoichiometric. The crystallization of the samples, however, has a strong dependence on the atomic percent of constituents of the prepared CZTS films. A single phase stannite-type structure CZTS with a large absorption coefficient of 10₄/cm in the visible range could be obtained after sulfurization at 520°C for 2 h. The samples relative to the RF magnetron sputtering showed a low resistivity of 0.073 Ωcm and band gap energy of about 1.53 eV. The samples relative to the ion beam sputtering exhibited a resistivity of 0.36 Ωcm and the band gap energy is about 1.51 eV. Supported by the National Natural Science Foundation of China (Grant No. 10574106), the Planned Science and Technology Project of Guangdong Province (Grant No.2003C05005) and the Natural Science Fund of Zhanjiang Normal University (Grant No.200801)     

Domain structure and defects of highly ordered Bi<Subscript>4</Subscript>Si<Subscript>3</Subscript>O<Subscript>12</Subscript> micro-crystals

Highly ordered Bi₄Si₃O₁₂ micro-crystals were prepared at normal atmosphere. Phase identification of the prepared crystals was accomplished by X-ray diffractometer (XRD). Domain structure and defects were characterized by environmental scanning electron microscopy (ESEM). XRD shows that the obtained micro-crystals are of eulytite structure with chemical formulation of Bi₄Si₃O₁₂. A highly ordered growth pattern is confirmed due to the faster growth of the {124} faces than that of the {204} faces by ESEM. The growing process of the domain structure is of pollen parent and filial generation pattern. The filial generations of Bi₄Si₃O₁₂ crystals are generated from the pollen parent. Cracks generate from the defect areas and propagate along the {124} faces due to their lower binding energy under a proper temperature gradient, contributing to the total transcrystalline fracture. It is confirmed that the generation and development of the voids in the crystal grains can be developed when unmatched dimensions of the two opposite faces are formed. And the development of the voids is dependent on the dimensions and orientations of the two opposite faces. Supported by the Innovation Research Team Funds of Shaanxi University of Science & Technology (Grant No. SUST-A04)     

Sensing characterization of Sn/In/Ti nanocomplex oxides for CO,CH<Subscript>4</Subscript> and NO<Subscript>2</Subscript>

The nanocomplex oxides of Sn-In and Sn-In-Ti were prepared by controlled co-precipitation method as sensing materials of semiconductor gas sensors for detection of CO, CH4 and NO2. Through manipulating the Sn/In cation ratio, metal salt total concentration, precipitation pH value and aging time, the nanocrystalline powders were successfully derived with chemical homogeneity and superior thermal stability, compared with the single component oxides. The particle size and morphology, surface area, and thermal and phase stabilities were characterized using TEM, TG-DTA, BET and XRD. The sensing tests showed that the Sn-In composites exhibit high sensitivity and selectivity for CO and NO2. The introduction of TiO2 enhanced CH4 sensitivity and selectivity, particularly, additives of Pd and Al2O3 as a dopant and surface modification greatly enhanced the sensing properties. The sensitivity depended on the composition of composites, calcination temperature and operating temperature. The optimal values were (25%In2O3- 75%SnO2)-20%TiO2 for ternary composite, 600 and 300℃, respectively. Temperature-programmed desorption (TPD) studies were employed to explain the gas adsorption behavior displayed by the surface of nanocomposites and X-ray photoelectron spectroscopic (XPS) analysis was used to confirm the electronic interactions existing between oxide components. The sensing mechanism of the nanocomposites was attributed to chemical and electronic synergistic effects.     

Synthesis and Characteristic of a New Niobate： BasNaCr0.5Nb9.5O30

A new niobate crystal was synthesized for the first time in BaO-NaO-Cr2O3-Nb2O3 system by the solid state reacition and the flux method. The new compound was studied by X-ray diffraction, electron probe, X-ray microanalysis, chemical analysis and SEM. The result of X-ray powder diffraction shows that Ba5NaCr0.5 Nb9.5O30 belongs to the tetragonal tungsten bronze structure, with space group P4 bin(100) and lattice parameters a=b=12. 4450 (2) A, c=3.9931 (2) A and Z=1. The X-ray powder diffraction lines of the compound were well indexed.     

Fabrication and magnetic properties of Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanocomposite permanent magnetic material

Sm3(Fe,Ti)29Nx/α-Fe dual-phase nanometer magnetic material was fabricated through rapid solidification, crystallization and nitridation of Sm-Fe (Ti) alloy. The effect of combination of rapid solidification and Ti alloy addition on the phase formation and microstructure of the Sm-Fe alloy is investigated in this paper. The microstructure of amorphous phase and dual-phase nano-grain crystals before and after crystallization annealing were observed using a high-resolution transmission electron microscope (HREM). The dual-phase nano-grains after annealing were compacted together with a clear interface with the direct exchange-coupling mechanism. Different annealing processes were used to examine the melt-spun alloy. Comparison of the images of SEM showed that annealing at 750℃ for 10 min was most suitable to get homogeneous and nano-grains. No obvious kink was detected in the second quadrant of the hysteresis loop like a single hard magnet, and strong exchange coupling was found between hard magnets and soft magnets.     

Interface structure of Ag (111)/SnO<Subscript>2</Subscript> (200) composite material studied by density functional theory

Electric contact material of Ag/SnO₂ was successfully synthesized by in situ process method. The interface structure was characterized by high-resolution transmission electron microscopy (HTEM) and simulated at atomic scale on computer. The mean-square displacements of atoms near the interface were calculated, and the results showed that near the interface both Ag side and SnO₂ were mismatched and this effect decays rapidly far from the interface. By inspecting the calculated density of states (DOS), we found that the electric-conductivity of this composite material was decreased because of the localized 4d and 2p electrons of Ag and O near the Fermi surface, respectively. Electron density changed acutely across the interface, so that there was no extra compound precipitated. A micro-electric field also formed in the whole material due to the interface structure, and this may affect the electron conduction and the related electric-conductivity of the composite. It is found that the interface cohesive energy of Ag (111)/SnO₂ (200) was −3.50 J/m², which is higher than the experimental results. Supported by the National Natural Science Foundation of China (Grant No. 2008CB617609), the Natural Science Foundation of Yunnan Province (Grant No. 2006E003Z) and Science Innovation Foundation of Kunming University of Science and Technology     

Preparation of Fe-Al Intermetallie /TiC-Al2O3 Ceramie Composites from llmenite by SHS

Fe-Al intermetallic/TiC-Al2O3 ceramic composites were successfully prepared by selfpropagating high-temperature synthesis （SHS） from natural ilmenite, aluminium and carbon as the raw materials. The effects of carbon sources, preheating time and heat treatment temperature on synthesis process and products were investigated in detail, and the reaction process of the FeTiO3-Al-C system was also discussed. It is shown that the temperature and velocity of the combustion wave are higher when graphite is used as the carbon source, which can reflect the effect of the carbon source structure on the combustion synthesis; Prolonging the preheating time or heat treatment temperature is beneficial to the formation of the ordered intermetallics; The temperature and velocity of the combustion wave are improved, but the disordered alloys are difficult to eliminate with the preheating time prolonged. The compound powders mainly containing ordered Fe3Al intermetallic can be prepared through heat treatment at 750 ℃.     

The Synthesis and Eleetrorheologieal Properties of BaTiO3-coated PMMA Mierospheres

Coated-PMMA microspheres consisting of poly （methyl methacrylate）（PMMA） core and barium titanate （BaTiO3） shell were synthesized by the modified sol-gel processing and then adopted as an electrorheological （ER） materials. The structure and morphology of coated powders were chyfecterized by SEM and FT-IR; the shear stress of the suspensions of coated-PMMA particles and pure PMMA particles in silicone oil with a 20 vol% were investigated. The results show that the BaTiO3 coated PMMA microspheres based suspension in silicone oil exhibited typical ER behavior and stronger ER effects.     

Nanocomposite films of V<Subscript>2</Subscript>O<Subscript>5</Subscript>−MoO<Subscript>3</Subscript> xerogel with poly ethylene oxide intercalation

Poly ethylene oxide (PEO)_x−V₂O₅−V₂O₅−MoO₃ (x=0, 0.5, 1) films were prepared by the sol-gel method. The synthesis and structure of the films were investigated by XRD, TG-DTA, FTIR, etc. The results show that V₂O₅−MoO₃ xerogel has a layered structure and its interlayer space increased from 1.3181 nm at x=0 to 1. 7898 nm at x=1 after the nanocomposite films were dried, and PEO in the interlayer changes the interface structure by forming hydrogen bonds with V=0 bands. CV measurement indicates that the intercalation of PEO improves insertion/extration properties of Li⁺ ions in the interlayer. ZHENG Jin-xia: Born in 1976 Funded by the National Natural Science Foundation of China (No. 50172036) and Natural Science Foundation of Hubei Province(No. 2001ABB083)     

Investigation of one-dimensional Si/SiO<Subscript>2</Subscript> hotonic crystals for thermophotovoltaic filter

The spectral control is widely incorporated with the thermophotovoltaic (TPV) technology to improve the optical-electric conversion efficiency of the whole system. In order to match with GaSb photovoltaic cell, an 8-layer one-dimensional photonic crystals (PC) filter structure was designed as quarter-wave periodic structure by selecting silicon (Si) and silicon dioxide (SiO₂) as candidate materials. The multilayer Si/SiO₂ structure was developed for the matching filter to simultaneously realize the optimal matching with the spectral distribution of the high temperature emitter and the quantum efficiency of GaSb cell. The physical vapor deposition (PVD) method was used to fabricate the optical filter and the normal incidence optical property of the filter was measured within the spectral range from 0.7 to 3.3 μm. These experimental data were used to predict the spectral control performance in a TPV system. Finally, temperature performance experiments were carried out to establish its withstanding performance in high temperature environment. Supported by the National Natural Science Foundation of China (Grant No. 50776047) and Natural Science Foundation of Jiangsu Province (Grant No. BK2007726)     

Nanomechanical Property Measurements of SrTiO<Subscript>3</Subscript> Submicron-fiber

Strontium titanate (SrTiO₃) submicron-fibers with perovskite structure were successfully synthesized by electrospinning method. The nanomechanical properties of synthesized SrTiO₃ were investigated by the novel amplitude modulation-frequency modulation (AM-FM) method based on atomic force microscope and nanoindentation technique. The results of AM-FM show that the resonant frequency of SrTiO₃ submicron-fiber is lower than that of the Si substrate, which indicates that the Young’s modulus of SrTiO₃ submicron-fiber is smaller than that of Si substrate in the range of 105–125 GPa. Nanoindentation further confirmed the results, showing a value of 104 ± 17 GPa. The atomic force microscope-based AM-FM provides us a new way to study the mechanical performance of low dimensional materials.     

Structure,Electrical Conducting and Thermal Expansion Properties of Ln0.6Sr0.4Co0.8Fe0.2O3 （Ln = La,Pr, Nd,Sm） Ceramics

Ln0.6Sr0.4Co0.2Fe0.2O3 （Ln=La, Pr, Nd, Sm） perovskite-type complex oxides were synthesized using a glycine-nitrate process, and the structure, electrical conducting and thermal expansion properties of the resulting ceramics were examined with regard to the nature of the lanthanide cations. The results indicated that the La, Pr and Nd specimens had a rhombohedral symmetry, while an orthorhombic structure was determined for the Sm specimen. The pseudo-cubic lattice constant decreased with smaller lanthanide cations. It was found that the electrical conducting properties declined with decreasing lanthanide cation size. Fortunately, all the compositions remained rather high electrical conductivities exceeding 650 Ω ^-1m·cm^-1 in the intermediate temperature range （600-800 ℃）. An appreciable thermal expansion increase at high temperatures was detected for all the compositions. Decreasing the size of the lanthanide cations resulted in an increase of thermal expansion. With respect to the high electrical conductivities, the Ln0.6Sr0.4Co0.8Fe0.2O3 oxides are considered to be acceptable as mixed conducting component in composite cathode designs together with doped ceria electrolytes.     

Straight SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanorod Y junctions

Novel straight silicon oxide [SiO _x (1<x<2)] nanorod Y junctions have been synthesized on Si plate by thermal evaporation of mixed powders of silica and carbon nanofibers at 1300°C and condensation on a Si substrate without assistance of any catalyst. The synthesized samples were characterized by means of scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, and energy dispersive X-ray spectroscopy. The results suggested that the straight nanorod Y junctions are amorphous and consist only of elements Si and O, and these rods with diameters about 50–200 nm have a neat smooth surface. The growth of such silicon oxide nanorods may be a result of the second nucleation on the surface of rods causing a change in the growth direction of silicon oxide nanorods developed. Supported by the Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing, and the Program of Science & Technology Activity for Chinese Homecoming Fellow Abroad and Research Program of Beijing Key Laboratory for Sensor (Grant No. KM200810772009)     

Effect of pH values on photocatalytic properties of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> synthesized by hydrothermal method

Highly crystalline orthorhombic Bi₂WO₆ powders were hydrothermally synthesized from aqueous solutions of Na₂WO₄ · 2H₂O and Bi (NO₃)₃ · 5H₂O over a wide range of pH. The effect of pH on morphologies, sizes and properties of the Bi₂WO₆ crystals was investigated. The band gaps of the as-prepared Bi₂WO₆ were determined from the onset of the absorption edge of UV-vis diffuse reflectance spectra. The methyl orange photodegradation was employed as a probe reaction to test the photocatalytic activity of the as-prepared samples under visible light irradiation. The photocatalytic activities of methyl orange degradation under visible light irradiation are strongly dependent on the pH used in the synthesis. The highest efficiency is observed at pH=7. Funded by the PCSIRT, the National Natural Science Foundation of China (Nos. 50532030 and 50625206) and the Zhejiang Provincial Natural Science Foundation of China (No. Z4080021)