Preparation,structure and dielectric properties of tungsten bronze ferroelectrics in SrO-Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were investigated.Both ceramics displayed weak frequency dependence in room temperature dielectric constant,which decreased from 125 to 118 for Sr4Eu2Ti4Nb6O30,from 206 to 195 for Sr5EuTi3Nb7O30 in the frequency range of 10 kHz to 1 MHz.The present ceramics showed a diffuse ferroelectric phase transition.The frequency independent transition temperature (Tm) indicated the above compounds had no relaxor property.The diffuseness (γ) was 1.45 and 1.64 for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.The weak ferroelectric of the present materials are indicated from the P-E hysteresis loops,and a small 2Pr of 0.596 μC/cm2 and 0.068 μC/cm2 were observed for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.     

Synthesis and characterization of a new Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> pillared triple-layered perovskite KSr<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>10</Subscript>

A n-Hexyl NH₃Sr₂Nb₃O₁₀ is obtained by the stepwise ion-exchange reaction, then is dispersed in aqueous solution of trinuclear acetato-hydroxo iron (III) nitrate, [Fe₃(OCOCH₃)₇OH·2H₂O]NO₃, and the interlayer potassium cations of the perovskite niobate are exchanged with the partially hydrolyzed trinuclear acetato complex ions. On heating, the exchanged complex ions are converted into iron oxide pillars which keep the perovskite sheets apart. The product is characterized by XRD, SEM, EDAX and surface area measurement respectively. Zhang Hui: Born in 1970 Funded by the National Natural Science Foundation of China (No. 50002007), Major Program of Ministry of Education (No. 0201) and Open Foundation of State Key Lab of Advanced Tech. for Materials Synthesis and Processing.     

Structure and dielectric properties of ZnO and Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> doped BaO-TiO<Subscript>2</Subscript> system microwave ceramics

The microwave dielectric properties and microstructure of BaTi4.3ZnyO9.6＋y ＋0.02 mol% SnO2＋0.01 mol% MnCO3＋x mol% Nb2O5（x=0-0.05, y=0-0.08） system ceramics were studied as a function of the amount of ZnO and Nb2O5 doped. Addition of （y=0-0.05） ZnO and （x=0-0.025） Nb2O5 enhanced the reactivity and decreased the sintering temperature effectively. It also increased the dielectric constant ε r and quality factor Q（=1/tan 8） of the system due to the substitution of Ti^4＋ ions with incorporating Zn^2＋and Nb^5＋ ions, which was analyzed by the reaction ZnO＋Nb2O5＋ 3 TiTxTi →ZnTi＋ 2NbTi＋3TiO2. When the system doped with （y=0.05） ZnO and （x=0.025） Nb205 were sintered at 1 160 ℃ for 6 h, the εr. Qf0 value and rfwere 36.5, 42 000 GHz, and＋1.8 ppm/℃, respectively, at 5 GHz.     

Synthesis and Dielectric Properties of New Niobate BiTi3Nb7O30

A new niobate Ba5 BiTi3Nb7O30 was synthesized by the solid-state reaction. It was characterized by X-ray diffraction and dielectric constant measurements. The results show that Ba5BiTi3Nb7O30 is paraelectric at room temperature and belongs to tetragonal 4/ mmm symmetry with unit cell parameters a = 1.25020 nm, c =0.39704 nm. Ba5BiTi3Nb7O30 has only one phase transition, paraelectric to ferroelectric, below 0℃.     

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.     

Preparation, Characterization and Dielectric Property of Sr5 LaTi3 Nb7O30 Ceramic

Sr5LaTi3Nb7O30 ceramic was prepared by the conventional high temperature solid-state reaction route. The sintered samples were characterized by X-ray diffraction, scanning electron microscopy ( SEM ), differential thermal calorimetry ( DSC ) and dielectric measurements. The results show Sr5LaTi3Nb7O30 belongs to paraclectric phase of filled tetrngonal TB structure at room temperature, and undergoes a diffuse phase transition in the temperature range of -54-34℃ . And Sr5LaTi3Nb7O30 ceramic shows a high dielectric constant of 479 with a low dielectric loss of 0.005 at 1MHz . In comparison with Ba-based ceramics with TB structure, the temperature coefficients of the dielectric constant ( τt ) is significantly reduced.     

Low-temperature sintering and microwave dielectric properties of Ba<Subscript>2</Subscript>Ti<Subscript>3</Subscript>Nb<Subscript>4</Subscript>O<Subscript>18</Subscript> ceramics

The effects of CuO and H3BO3 additions on the low-temperature sintering,microstructure,and microwave dielectric properties of Ba2Ti3Nb4O18 ceramics were investigated.The addition of less amount of CuO (< 1 wt%) considerably facilitated the densification of Ba2Ti3Nb4O18 ceramics.Appropriate addition of H3BO3 (< 3.5 wt%) remarkably improved the microwave dielectric properties of ceramics.The addition of H3BO3 and CuO successfully reduced the sintering temperature of Ba2Ti3Nb4O18 ceramics from 1300 to 1050 ℃.B...     

Hydrothermal preparation and photocatalytic water splitting properties of ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript>

ZrW₂O₈ was prepared by adjusting Zr:W mole ratio and HCl concentration in hydrothermal reaction processes. The obtained sample was crystallized in α-ZrW₂O₈ phase (cubic, P2₁3), with band gap energy of 4.0 eV. The properties of photocatalytic water splitting were examined under UV light irradiation. The average rate of H₂ evolution over 0.3wt% Pt/ZrW₂O₈ in the presence of CH₃OH as electron donor (ED) was 23.4 μmol/h, while the average rate of O₂ evolution over ZrW₂O₈ in the presence of AgNO₃ as electron scavenger (ES) was 9.8 μ mol/h. Moreover, H₂ was evolved over 0.3wt% Pt/ZrW₂O₈ from pure water splitting at a rate of 5.2 μ mol/h. The study indicated that the band structure of ZrW₂O₈ was suitable for reducing H⁺ to H₂ and oxidizing H₂O to O₂. The band structure and photocatalytic water splitting properties of ZrW₂O₈, different from either ZrO₂ (5.0 eV) or WO₃ (2.7 eV), were attributed to the hybridization of W5d and Zr4d in conduction band (CB) as well as the change in crystal structure.     

Molten Salt Synthesis of Ba（ Mgl／3Nb2／3 ）O3 Powder

The single-phrase Ba(Mgl/3Nb2/3)O3(BMN) powder was saccessfully prepared by the KCImolten salt synthesis(MSS) method. The temperature for single-phase BMN powders by MSS was about 400℃ lower than that by the solid-phase method. The average particle size (APS) was about 0.91,u.m at 900℃ and increased with increasing synhesis temperature. Based on the APS, the activation energy for particle growth in theMSS, whose value was 64. 1kJmol^-1.was attained. The sinterability of the powder prepared by MSS method wasbetter than that pretared by solid-phase method.     

Effect of ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass addition on the microwave dielectric properties of BaO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The effect of ZnO-B₂O₃(ZB) glass addition on the sintering behavior, microstructures and microwave dielectric properties of BaO-Nd₂O₃-TiO₂-Bi₂O₃ (BNTB) system was investigated with the aid of X-ray diffraction, scanning electron microscopy and capacitance meter. It is found that the ZB glass addition, acting as a sintering aid, can effectively lower the sintering temperature of BNTB system to 850 °C. The dielectric constant of BNTB-ZB ceramics increases with the increase of soaking time and the value of dielectric loss decreased with increasing soak time. The optical dielectric properties at 1 GHz of ɛ=74, tan δ=4×10⁻⁴, and TCC=25 ppm/°c were obtained for the BNTB system doped with 25 wt% ZB glass sintered at 850 °C for 2 h, representing that the BNTB-ZB ceramics could be promising for multilayer low temperature co-fired ceramics applications.     

Novel preparation and XPS analysis of V<Subscript>2</Subscript>O<Subscript>5</Subscript> xerogel

The V₂O₅ sol was fabricated by ultra-fast quenching. The vanadium with low valence (V⁴⁺) was found in V₂O₅ xerogel films by XPS analysis. The technology of oxygen top-blown was applied to analyze the XPS spectrum difference of V₂O₅ xerogel when the powder of V₂O₅ was melting in air or in oxygen atmosphere. The results show that the different melting atmosphere has certain influences on the chemical valence of V₂O₅ xerogel. ZHU Quan-yao: Born in 1968 Funded by the National Natural Science Foundation of China (No. 50172036, No. 59802009)     

Thermoelectric Properties and Electronic Structure of Ca3Co2O6

The nanosized Ca3Co2O6 powder was synthesized via sol-gel process.The phase composition was characterized by means of X-ray diffraction.Polycfrystalline swnples of Ca3Co2O6 were prepared by a sintering procedure of nanosized power.The seebeck cofficient and electrical conductivity of the samples were measured from 450K up to 750 K.The results show that the Seebeck coefficient increases with the increasing temperature.The electronic structures were calculated using the self-cwtsistent full-potential linearized augmentedc plane-wave (LAPW) method within the density functional theory.The relationship between thermoelectric property and electronic structures was discussed.     

Solid Solution Characteristics of Pb（B1/3Nb2/3）O3-bascd Composite Ceramics

The solid solution characteristics of Pb（B1/3Nb2/3）O3-based （B=Zn^2＋, Mg^2＋, Ni^2＋） composite ceramics prepared by two-phase mixed-sintering method were developed based on dielectric measurements. Results show that there are double dielectric peaks for PZN-based composite ceramic, implying two phases coexist. However single dielectric peak was presented in PMN- and PNN-based composite ceramics, respectively. It is indicated that obvious solid solution reaction exists during the sintering process of these two systems. The effects of B-site ion difference on the solid solution characteristics were discussed by crystal chemistry. SEM was employed to investigated the microstructures of composite ceramics. The influences of solid solution reaction on grain growth were discussed.     

Preparation and characterization of nanocomposite MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript>

Nanocomposites MgFe₂O₄/SiO₂ were successfully synthesized by the sol-gel method in the presence of N, N-dimethylformamide (DMF). The formation of pure MgFe₂O₄ was confirmed by powder X-ray diffraction (XRD) and electron diffraction. The structural evolution of MgFe₂O₄ nanocrystals was followed by powder X-ray diffraction and IR absorption spectroscopy. The formation of spinel structure of MgFe₂O₄ started at 800 °C, and completed at 900 °C. The transmission electron microscopy (TEM) measurements suggest that the particle sizes increase with the increasing annealing temperature, and the mean particle sizes of the spherical samples annealed at 800 °C, 900 °C and 1 050 °C are ca. 3 nm, 8 nm and 11 nm, respectively. Magnetization measurements at room temperature and 78 K indicate superparamagnetic nature of these MgFe₂O₄ nanocrystals. Funded by the National Natural Science Foundation of China(No. 30771676), the Natural Science Foundation of Jiangsu Province (No. BK20081842), and the Foundation of Nanjing Bureau of Personal for the Returned Overseas Chinese Excellent Scholars     

Effect of aluminum addition on microstructure and properties of SiO<Subscript>2</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CaO vitrified bond

Influence of aluminum addition on the structures and properties of SiO₂-B₂O₃-Al₂O₃-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10^-6 °C^-1, respectively.     

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)     

Glass formation and optical band gap studies on Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO ternary system

The glass forming region of Bi₂O₃-B₂O₃-BaO ternary system was investigated. A serial of glass samples with high Bi₂O₃ content in Bi₂O₃-B₂O₃-BaO system were prepared by using conventional melting and quenching meld, and the refractive indexes and absorption spectra of samples were measured. It is found that the refractive index of samples as well as the UV absorption increase with the increase of BaO content. According to the Tauc law, optical band gap E _opg which is assumed to be the effective energy band gap E _g is calculated and decreases with the increasing BaO content, and the ratio of E _g/E _opg is 1.3.     

Optical and magnetic properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> nano-composite films

Fe₂O₃/SiO₂ nano-composite films were prepared by sol-gel technique combining heat treatment in the range of 100–900 °C. The particle size was observed by FE-SEM. Optical properties of the films were investigated by UV-visible spectra. Structural and magnetic characteristics were investigated through FT-IR and VSM. The transparency of the Fe₂O₃/SiO₂ nano-composite films decreased with the content of the Fe₂O₃. Water and organic solvent in the films were evaporated with heat treatment, so the transparency of the films was enhanced under high temperature. It is also found that the saturation magnetization (M _s) of the films increases with the temperature. As the content of the Fe₂O₃ increases, when the content of the Fe₂O₃ is around 30wt%, the M _s of the films has a maximum value.     

Effect of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> on structure and properties of calcium aluminate glasses

The effect of Ga₂O₃ on the structure and properties of calcium aluminate glasses fabricated by vacuum melting process was investigated by Raman spectrum, differential scanning calorimeter (DSC), and infrared spectrum methods. The results show that calcium aluminate glass network only consists of [AlO₄] tetrahedral units. With the gradual addition of Ga₂O₃, the quantity of [GaO₄] tetrahedral units increases. Substitution of Ga₂O₃ for Al₂O₃ results in a decrease in T _g T _x, and T _p, and an increase in the thermal stable index ΔT. Similarly, the absorption band around 3.0 μm obviously reduces and the transparency in 4.0-6.0 μm rapidly increases with increasing Ga₂O₃ content. However, the chemical stability of calcium aluminate glasses decreases if Ga₂O₃ is introduced due to the increasing of [GaO₄] units in the glass network.     

Structure and properties of Mg-doped SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> Bi-layered compounds

The structure and properties of Mg-doped SrBi4Ti4O15（SBT） were dicussed. Mg substitution into SBT had two possibilities states with the dopant amount variety. Mg cation substituted mostly into Sr^2＋ and the amount proportion was 68.11%.Mg ion will substitute into Ti ion site in perovskite layer when the doping amount increases. Polarization increases sharply when x=0.1 and then decreases becauses of the domain pinning. The Curie temperature of Mg-doped SBT is about 300 ℃ and there is a broad diffuse phase transition near Tc with a flat peak near the Ta of SBT.