Hydrothermal Synthesis of the Blue Potassium Molybdenum Bronze, K0.28MoO3

Blue potassium molybdenum bronze, K_0.28MoO₃, was prepared by hydrothermal heating hydrogen molybdenum bronze in KCl solution at 431 K. Hydrated molybdenum bronze was found formed as an intermediate during the conversion from hydrogen molybdenum bronze to blue bronze. The hydrothermal method proved itself an easy and effective for synthesis of mixed-valence compounds.     

Physical and Electrochemical Characterization of Hydrothermal Prepared α'-NaV_2O_5 Crystals

α'-NaV2O5 was prepared by a simple hydrothermal process.X-ray diffraction confirmed the orthorhombic structure of α'-NaV2O5,with preferential growth along the (001) direction.Scanning electron microscopy showed α'-NaV2O5 was composed of flake-shaped crystals.X-ray photoelectron spectroscopy confirmed the co-existence of V4+ and V5+ in α'-NaV2O5,which results in an average V4.5+ oxidation state of α'-NaV2O5.The observed Raman bands are ascribed to different V―O vibrations.α'-NaV2O5 shows a reversible specific capacity of about 100 mA·h·g-1 between 3.5 and 1.0 V,with a good capacity retention.The good electrochemical stability of the material is attributed to its structural stability during Li+ intercalation.     

New high permittivity tetragonal tungsten bronze dielectrics Ba2LaMNb4O15: M=Mn, Fe

The new phases Ba₂LaMNb₄O₁₅: M=Mn, Fe were prepared by solid state reaction at 1100 °C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90±15 over the range 10-320 K. Ba₂LaFeNb₄O₁₅ is highly insulating with bulk conductivity ?10⁻⁸ ohm⁻¹ cm⁻¹ at 25 °C and tan δ?0.001 over the range 100-320 K and at 10⁵ Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba₂LaTi₂Nb₃O₁₅ show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti⁴⁺ by a mixture of (Mn, Fe)³⁺ and Nb⁵⁺.     

Raman characterization of Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) solid solutions

The ferroelectric compounds Pb₂Na_1−xLa_xNb_5−xFe_xO₁₅ and Pb_0.5(5−x)La_xNb_5−xFe_xO₁₅ (0≤x≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200-1000 cm⁻¹ three main A₁ phonons around 240 (υ₁), 630 (υ₂) and 816 (υ₃) cm⁻¹ were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm⁻¹, reveals a structural change in the studied solid solutions. The behaviour of the Raman shift of the υ₁ mode confirms that in Pb₂Na_1−xLa_xNb_5−xFe_xO₁₅, a clear anomaly occurs in the vicinity of x=0.4.     

Barium Sodium Niobate Powders and Thin Films: Preparation and Ferroelectric Behavior

Powders and thin films of barium sodium niobate, Ba₄Na₂Nb₁₀O₃₀, of filled tungsten bronze type ferroelectric were processed by a sol-gel route using barium metal, niobium ethoxide and sodium methoxide as precursors. Polycrystalline powder resulted after heat treating the gel powder at or above 650°C. Thin films of Ba₄Na₂Nb₁₀O₃₀ showed no preferred orientation on Si(100), Pt/Si(100) and sapphire substrates. Hysteresis measurements at 1 kHz for the thin films annealed at 750°C, obtained using a prehydrolyzed precursor solution, and gave remanent polarization of 17.34 µC/cm² and coercive field of 62.5 kV/cm. Microstructural investigation of surface morphology of these films revealed grains about 0.3 µm in size. Prehydrolysis of the precursor solution was found to be necessary to achieve dense films with ferroelectric properties.     

准二维电荷密度波导体钾紫青铜KxMo6O17单晶样品的制备

采用碳酸盐替代高钼酸盐电解还原的方法成功制备出了准二维电荷密度波导体钾紫青铜单晶.通过x射线衍射、透射电子显微术等方法对单晶进行结构分析表明：晶胞参数a=b=0.5540nm，c=1.3508nm，单晶为三角晶系，对称群为P3.电阻温度关系曲线的测量显示：钾紫青铜K_xMo₆O₁₇单晶在112K附近发生金属到金属的Peierls相变. 关键词： 钾紫青铜 电荷密度波 Peierls相变     

云南青铜防腐显微拉曼光谱和EPMA研究

应用显微激光拉曼光谱和EPMA(电子探针技术),对云南的四件青铜器(两件春秋时期的青铜矛和两面元代的青铜镜)的腐蚀情形和防腐技术进行了分析研究。拉曼实验结果表明,云南青铜器表面腐蚀产物的主要成分有Cu2O和CuCO3.Cu(OH)2。利用电子探针技术,确定了青铜器内部和表面的元素成分。本文初步分析了云南四件青铜器防腐技术的应用和发展,春秋战国时期,人们在青铜矛表面涂上一层锡的氧化物涂层以防腐蚀;元代的人则采用合金表面处理技术防腐。事实证明,锡的氧化物涂层的防腐效果最好。对金属文物的研究,显微激光拉曼光谱是一种原位无损检测的有效方法,但还是有某些局限性,若配合以电子探针等测试方法,可以达到更好的效果。     

Microstructure evolution and dielectric properties of Ba<Subscript>5-x</Subscript>Na<Subscript>2x</Subscript>Nb<Subscript>10</Subscript>O<Subscript>30</Subscript> ceramics with different Ba–Na Ratios

The tetragonal tungsten bronzes of Ba5−xNa_2x Nb₁₀O₃₀ (BNN, 0.5≤ x≤1.3) ceramics were synthesized using the solid state reaction method. The sintering behavior and dielectric characteristics of the BNN ceramics, as a function of the Ba-Na ratio, were examined. Densification of the samples with excess compositions of Ba and Na was higher than that of the stoichiometric BNN sample. The maximum dielectric constant and the Curie temperature showed highest values at the stoichiometric composition and decreased as the composition shifted away from the stoichiometry. in order to obtain a quantitative evaluation of the diffuse phase transition (DPT) behavior of the BNN ceramics, γ and C/κ_max were calculated. The weakest DPT behavior was observed in the stoichiometric composition. An increase in the DPT is in correlation with the increase in the number of ways of cation distribution by the disordered occupation of Ba and Na and the vacancies in the A1 and A2 sites of the tungsten bronze structure.     

Crystal chemical and dielectric study of niobochromates with the tungsten bronze structure

Abstract

A crystal chemical study has allowed us to identify new niobochromates crystallizing with the tungsten bronze structure: Ba₂LnNb₄CrO₁₅ (Ln = Bi, La), La₂ANb₄CrO₁₅ (A = Li, Na, K) and Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅ (0 ? x ? 1). A dielectric study has shown that the T _c (x) curve goes through a minimum at x ? 0.5 along the solid solution Ba₂Na_1-x La _x Nb_5-x Cr _x O₁₅, while the ferroelastic transition T_c changes very slightly in the same range of composition.