钨青铜结构Ba6Zn0.67M9.33O30(M=Nb,Ta)的合成与介电特性

Two compounds Ba₆Zn_0.67M_9.33O₃ and Ba₆Zn_0.67M_9.33O₃₀ with tungsten bronze structure were synthesized in the BaO-ZnO-Nb₂O₅/Ta₂O₅ systems by the conventional high temperature solid-state reaction.The structure and dielectric properties of Ba₆Zn_0.67M_9.33O₃ and Ba₆Zn_0.67M_9.33O₃₀ were determined by X-ray powder diffraction,scanning electron microscope and dielectric measurements.The results show that Ba₆Zn_0.67M_9.33O₃₀ belongs to paraelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters a:1.26256(4) nm, c:0.39698(2) nm. The room temperature dielectric constant (ε) of Ba₆Zn_0.67M_9.33O₃₀ ceramic reached 108 combined with a low dielectric loss of 0.005 at 1 MHz. While Ba₆Zn_0.67M_9.33O₃ belongs to fully filled tetragonal tungsten bronze structure at room temperature with the unit cell parameters a:1.25940 (3) nm, c=0.40008(2) nm. Ba₆Zn_0.67M_9.33O₃₀ ceramic shows significant relaxor behaviors, and the phase transition from ferroelectric to paraelectric occurred at 55℃ (at 1 MHz). The room temperature dielectric constant (ε) of ceramic reached 570 at 1 MHz.     

类钙钛矿新铌酸盐Ba6LaTi3Nb3O21的合成、结构与介电特性

A New Niobate Ba₆LaTi₃Nb₃O₂₁ was synthesized by high temperature solid state reaction in the BaO-La₂O₃-TiO₂-Nb₂O₅ system. The chemical compositions, crystal structure, microstructure, density and melting point of the new compound were characterized by EPMA, XRD, DTA and so on. Ba₆LaTi₃Nb₃O₂₁ crystallizes the rhombohedral system with unit cell parameters a=0.57388(2) nm, c=4.928 3(3) nm, and space group R3m, Z=3. The structure may be described as six (Nb,Ti)O₆ octahedra corner-sharing along c-axis to form perovskite layer connected by Ba atoms. The Ba₆LaTi₃Nb₃O₂₁ ceramics exhibits high dielectric of 74.1, low dielectric loss of 4.7×10^-4 and small temperature coefficient of dielectric constant of -69 ppm·K^-1 at 1 MHz due to its close structure and relative high dielectric polarizabilities of Ba²⁺, La³⁺, Ti⁴⁺ and Nb⁴⁺. Ba₆LaTi₃Nb₃O₂₁ might be a suitable candidate of high ε_r microwave dielectric ceramics.     

类钙钛矿新铌酸盐Ba4LaTiNb3O15的合成、结构与介电特性

A new niobate compound Ba₄LaTiNb₃O₁₅ has been synthesized and characterized. Through Rietveld refinement of X-ray powder diffraction data, Ba₄LaTiNb₃O₁₅ is identified as the A₅B₄O₁₅ type cation-deficient perovskites with space group of P3m1(164) and lattice constants a=0.572 38(1) nm, c=1.169 48(1) nm, V=0.331 81(1) nm³, and Z=1. The crystal structure can be described as consisting of identical perovskite-like blocks, four corner-sharing (Ba,La)O₆ octahedra thick, separated by layers of vacant octahedral. The (Ba,La)-O bond lengths range from 0.267 to 0.321 nm and the (Ti,Nb)-O bond lengths range from 0.175 to 0.213 nm. The Ba₄LaTiNb₃O₁₅ ceramic has a high dielectric constant of 53.3, high quality factors (Q) 3 650 (at 6.402 5 GHz), and low temperature variation of resonant frequency (τ_f) +69.3 × 10^-6 K^-1.     

PMW-PNN-PT陶瓷的制备及介电性能研究

0.29Pb(Mg_1/2W_1/2)O₃-0.41Pb(Ni_1/3Nb_2/3)O₃-0.30PbTiO₃ ＋ 0.002 5MnO₂＋xWO₃(PMW-PNN-PT) ceramics were prepared by Semichemical Method. The Mg(Ac)₂, Ni(Ac)₂, and Mn(NO)₃ solution rather than MgO, NiO and MnO₂ were added to the slurry of PbO, WO₃, Nb₂O₅ and TiO₂ and then calcined at 850 ℃ for 2 h. Then the sample was sintered at 1 100～1 200 ℃ for 2 h. The effect of sintering temperature and WO₃-excess amounts on the phase constitute, microstructure and the dielectric characteristics was investigated. The result showed that the PMW-PNN-PT powders with pure pervoskite phase were prepared by single-step calcination. The development of sintered temperature contributes to the increase of dielectric constant and the flatness of dielectric temperature dependence. But the dielectric properties will be worse if the sintered temperature is too high. The increase of WO₃-excess level lead to an increase of Pb₂WO₅ phase and the flatness of dielectric curves, but the dielectric constant will be decreased. The proper WO₃-excess amount of X7R type PMW-PNN-PT ceramics is 5mol% and the proper sintering condition is 1 150 ℃ for 2 h, the maximum dielectric constant is 5 395.     

Eu3+在Ba2TiSi2O8中的发光

The barium titano-silicate phosphors doped with Eu³⁺ were synthesized by high temperature solid state reaction. The structures of as-synthesized samples were characterized by powder XRD. The maximum peaks of emission spectra of Ba₂TiSi₂O₈ and Ba₂TiSi₂O₈∶Eu³⁺ were respectively located at 450 and 618 nm, coming from the transitions of charge-transfer bands of Ti⁴⁺-O^2- and forced electric-dipole transition ⁵D₀-⁷F₂ of Eu³⁺. The luminous mechanisms of Ba₂TiSi₂O₈ and Ba₂TiSi₂O₈∶Eu³⁺ were suggested. The effects of concentration of Eu³⁺ on the luminous performance of Ba₂TiSi₂O₈∶Eu³⁺ were also studied and the results showed that the optimum concentration of Eu³⁺ was 0.12 mol per mole of matrix.     

Nd2O3添加量对BaTiO3陶瓷介电性能的影响

BaTiO₃ ceramics doped with Nd₂O₃(the additive content was respectively 0.001,0.002,0.003,0.005,0.01,0.03mol)were prepared by Sol-Gel method. Effects of Nd₂O₃ contents on the dielectric constant (ε), the dielectric loss (tanδ) ,the Curie-temperature (T_C) and the resistivity (ρ) of BaTiO₃ ceramic were studied. When Nd₂O₃ content was 0.001mol and 0.002mol, the dielectric constant was increased obviously, but the dielectric loss was also increased. When Nd₂O₃ content was 0.003mol, the dielectric constant was increased, and the dielectric loss was decreased, which was suitable for application in condenser. The resistivity was decreased obviously with the increasing of Nd₂O₃ contents, the resistivity was the smallest when Nd₂O₃ content was 0.001mol. The Curie-temperature was also decreased with the increasing of Nd₂O₃ contents.     

Ba1-xSrxTi1-yMyO3固溶体的湿化学法合成与介电特性

A series of Ba_1-xSr_xTi_1-yM_yO₃ (M=Zr,Sn, 0≤ x≤ 0.5,0≤ y≤ 0.3) solid solutions were synthesized by chemical method at below 100℃ . XRD and cell parameters component figures of the series of the solid solutions powder demonstrated that the compounds are mutually miscible in the solid solutions. The particls size is about 70nm with spherical shape and uniform distribution. The result of preparing ceramics showed that after adulterating with Sr²⁺ and Zr⁴⁺ or Sn⁴⁺ in pure BaTiO₃ phase, the dielectric constant increased eight times while the dielectric loss decreased three times at room temperature.     

BaO-Al2O3-B2O3系密封玻璃的结构与性质

The BaO-Al₂O₃-B₂O₃ glasses manufactured for solid oxide fuel cell(SOFC) sealing were studied. The effect of different n_BaO/n_B2O3 on crystal, thermal properties, density and infrared spectra of this system has been discussed. The results show that the trends of crystallization, glass transformation temperature, dilatometric softening temperature and density increase with n_BaO/n_B2O3 values. But a typical property deviation occurs when n_BaO/n_B2O3 is 0.875, and its coefficient of thermal expansion has the maximum at this point. The changes of properties can attribute to the conversion of boron from tetrahedral coordination to trigonal, breakage of the local glass network and interaction between the network modifiers. These can be proved by infrared spectra of glasses. Thermal properties of some studied samples are suitable for the sealing of SOFC using Sm doped ceria electrolyte and operating at 400～600 ℃.     

Mn位掺杂钙钛矿结构化合物LaSr2Mn2-xNixO7的磁性和电性的研究

The effect of Ni substitution for Mn on magnetic and transport properties has been investigated for layered manganese oxides LaSr₂Mn_2-xNi_xO₇. Nickel doping hampered the canted antiferromagnetic (AFM) exchange at low temperature and their Neel temperature (T_N) decreased from 138 K (x=0) to 102 K (x=0.3). Meanwhile, spin glass, charge ordering and metal-insulator transition are suppressed by Ni addition. The resistivity increases obviously with increasing x due to double exchange interaction channel broken by Ni²⁺ addition. The resistivity of all samples in low temperature range fits to the Mott′s variable rang hopping (VRH) model, while it fits to nearest neighbor hopping of small polarons model in high temperature range.     

球形La2O3∶Eu纳米晶的制备及其发光特性

The spheric La₂O₃∶Eu nanocrystals were prepared using NH₃·H₂O-NH₄HCO₃ mixture as precipitant. The material was characterized by FTIR, XRD and TEM techniques. The luminescence properties of Eu³⁺ in spheric La₂O₃ were measured by three dimension spectra, emission and excitation spectra. The results indicate that the La₂O₃∶Eu nanocrystals are in hexagonal phase by annealing at 800 ℃, the crystal size is about 30 nm. The maximum emission and excitation wavelength were determined by three dimensional spectroscopy to be at 591 nm and 394 nm, respectively. In emission spectrum the band at 591 nm and 612 nm are corresponding to ⁵D₀-⁷F₁ and ⁵D₀-⁷F₂ transition of Eu³⁺ ions. With increasing in annealing temperature the differences of intensity of the two transitions are increased. This phenomenon shows that the luminescence intensity of La₂O₃∶Eu nanocrystals can be tuned by changing annealing temperature.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

KCl-KBO2-K2CO3, K2MoO4-KBO2-K2CO3, and K2WO4-KBO2-K2CO3 ternary systems

phase diagrams of KCl-KBO₂-K₂CO₃, K₂MoO₄-KBO₂-K₂CO₃, and K₂WO₄-KBO₂-K₂CO₃ ternary systems were studied by a calculation-experimental method and differential thermal analysis (DTA). The coordinates of ternary eutectics were determined to be E ₁: 622°C, 8.5 mol % KBO₂, 56.5 mol % KCl, and 35 mol % K₂CO₃; E ₂: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂MoO₄; E ₃: 710°C, 23 mol % KBO₂, 43 mol % K₂CO₃, and 34 mol % K₂WO₄. The specific heats of melting of the eutectics were determined.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

Solubility in the Na2Cr2O7-(NH4)2Cr2O7-K2Cr2O7-H2O system

Solubility in the Na₂Cr₂O₇-(NH₄)₂Cr₂O₇-K₂Cr₂O₇-H₂O four-component water-salt system at 25, 50, and 75°C was studied for the first time. Phase field boundaries for individual salts and potassium and ammonium dichromate solid solutions, monovariant lines, and invariant points were determined. Experimental data were used to optimize the looped isohydric process of potassium dichromate preparation involving additional salts.     

Li2SO4-Na2SO4-H2O和Li2SO4- K2SO4-H2O溶液的体积性质

本文用高精度数字式振荡管密度计测定了288K至318K温度范围内Li₂SO₄ + Na₂SO₄ + H₂O和 Li₂SO₄ + K₂SO₄ + H₂O三元体系的密度。混合溶液的离子强度范围从0.1到4.5 mol.kg_–1,混合溶液中Na₂SO₄和K₂SO₄的离子强度分数为0.2,0.4,0.6和0.8。用密度实验值拟合得到了不同温度下Pitzer离子相互作用模型混合参数θ_V和 ψ_V,模型的计算值与实验值的偏差在±0.002 g.cm_–3以内。用Pitzer模型计算了不同离子强度下三元体系的混合体积。     

NaBO2-NaCl-Na2CO3, NaBO2- Na2CO3-NaMoO4, NaBO2- Na2CO3-NaWO4, and NaBO2-NaCl-Na2WO4 ternary systems

The phase diagrams of the NaBO₂-NaCl-Na₂CO₃, NaBO₂-Na₂CO₃-Na₂MoO₄, NaBO₂- Na₂CO₃-Na₂WO₄, and NaBO₂-NaCl-Na₂WO₄ ternary systems were studied by a calculation-experimental method and differential thermal analysis. The coordinates of ternary eutectics were determined: E ₁: 612°C, 16 mol % NaBO₂, 42 mol % NaCl, and 42 mol % Na₂CO₃; E ₂: 568°C, 12 mol % NaBO₂, 28 mol % Na₂CO₃, and 60 mol % Na₂MoO₄; E ₃: 575°C, 12 mol % NaBO₂, 32 mol % Na₂CO₃, and 56 mol % Na₂WO₄; E ₄: 628°C, 8 mol % NaBO₂, 20 mol % NaCl, and 72 mol % Na₂WO₄; and E ₅: 655°C, 9 mol % NaBO₂, 53 mol % NaCl, and 38 mol % Na₂WO₄.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.     

SnSbBiS4-SnS and SnSbBiS4-Sn2Sb6S11 sections of the SnS-Sb2S3-Bi2S3 ternary system

SnSbBiS₄-SnS and SnSbBiS₄-Sn₂Sb₆S₁₁ sections were studied by physicochemical methods (DTA, X-ray powder diffraction, microstructure observation, and microhardness measurements). These sections were found to be eutectic quasi-binary sections of the SnS-Sb₂S₃-Bi₂S₃ ternary system. Solid solution regions based on the initial components were found on either side of the sections. Alloys in the solid solution region are p-type semiconductors.     

Theoretical study of polyoxide clusters B20O30, Al20O30, V20O50, Si20O30H20, and Si20O30F20

The structural, electronic, and vibrational characteristics and energies of the isolated polyoxide clusters B₂₀O₃₀, Al₂₀O₃₀, V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀ and their complexes with the H⁻ ion and ammonia complexes Al₂₀O₃₀ · nNH₃ have been calculated by the density functional theory B3LYP method with different basis sets. The computation results show that the symmetric closo structure I _h with oxygen bridges located above the centers of the faces of an empty [M₂₀] dodecahedron is more favorable for V₂₀O₅₀, Si₂₀O₃₀H₂₀, and Si₂₀O₃₀F₂₀. For B₂₀O₃₀, the cage closo isomer is also more favorable than the other isomers, but its structure is severely distorted as compared to a dodecahedron and has a symmetry close to C ₃ . For Al₂₀O₃₀, the I _h structure corresponds to a high-lying local minimum of the potential energy surface. For Al₂₀O₃₀, a set of unusual puckshaped isomers of symmetry C _i , with different numbers of four-coordinate atoms ^IVAl and three-coordinate atoms ^IIIO, was localized; these structures are more than 90 kcal/mol more favorable than the dodecahedron I _h . The most favorable isomer of Al₂₀O₃₀ contains twelve four-coordinate atoms ^IVAl and four five-coordinate atoms ^VAl. The energies of dissociation of the most favorable M₂₀O₃₀ clusters into the M₂O₃ (C _2v ) and M₄O₆ (T _d ) fragments and, in the case of Al₂₀O₃₀, also into the Al₈O₁₂ (O _h ) and Al₁₂O₁₈ (D _3d ) fragments, have been estimated. The conclusion has been drawn that these clusters can, in principle, exist and can be experimentally detected in the isolated state. Analogous calculations have been performed for ammonia complexes Al₂₀O₃₀ · nNH₃ with n varying from 1 to 20. The effect of solvation on the relative stability of the dodecahedral and puckshaped isomers of the Al₂₀O₃₀ cluster is observed. The isomers with ammonia molecules in their first coordination sphere become much closer to one another on the energy scale; however, the dodecahedron remains a considerably less favorable intermediate. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 4, pp. 624–635.     

Extension of the La7Mo7O30 structural type with La7Nb3W4O30 and La7Ta3W4O30 compounds

Two compounds of formula La₇A₃W₄O₃₀ (with A=Nb and Ta) were prepared by solid-state reaction at 1450 and 1490 °C. They crystallize in the rhombohedric space group R-3 (No. 148), with the hexagonal parameters: , and , . The structure of the materials was analyzed from X-ray, neutron and electronic diffraction. These oxides are isostructural of the reduced molybdenum compound La₇Mo₇O₃₀, which are formed of perovskite rod along [111]. An order between (Nb, Ta) and W is observed.