Luminescence of Ba3SrM2O9 (M = Nb,Ta)

The Nb₂O₉^8? and Ta₂O₉^8? complexes show efficient luminescence at low temperatures in Ba₃SrM₂O₉ (M = Nb, Ta). This is in line with earlier predictions. Emission and excitation spectra are reported and discussed. The Cr³⁺ ion in these complexes shows ²E emission. Its crystal field is strong. It is shown that CrNbO₉^10? and CrTaO₉^10? complexes are responsible for the spectra observed.     

Preparation and photoconduction of rapidly quenched films in the Bi2O3-TiO2 system

The rapidly quenched films in the Bi₂O₃-TiO₂ system (0 to 60% TiO₂) were prepared using a twin-roller type apparatus. The films precipitated Bi₂O₃ solid solutions of different types in the composition ranges, with TiO₂ contents of 0 to 5, 7.5 to 10 and 12.5 to 40%, respectively. The first solid solution had a tetragonal structure of -form. The second, though also crystallized in the tetragonal structure, adopted a disordered modification of the -form. The third solid solution was -form (defect fluorite structure). The formation of amorphous phase commenced in the composition with 30% TiO₂, and the films became completely amorphous beyond 50% TiO₂. The quenched films showed a certain instability to decompose or transform into the different phase assemblage by annealing at higher temperatures (about 400 to 500° C, except 260° C for the pure Bi₂O₃ film). The quenched films were also characterized by a high photoconductivity. The photoconduction mechanism was suggested to be associated with a structural imperfection of Bi₂O₃ accompanied by a certain amount of pentavalent bismuth ion.     

Synthesis and structural characterization of (Bi2O3)1?x (Y2O3)x and (Bi2O3)1?x (Gd2O3)x solid solutions

Solid solution series, (Bi₂O₃)_1−x (Y₂O₃)_x and (Bi₂O₃)_1−x (Gd₂O₃)_x, forx = 0.10, 0.20, 0.30 and 0.40 were synthesized by standard ceramic technique. The structural phase characterization was carried out using X-ray powder diffraction technique. It was found that the solid solution containing 20–40 mole% of Y₂O₃ had face-centred cubic structure. All samples of the solid solution series, (Bi₂O₃)_1−x (Gd₂O₃)_x, had rhombohedral single phase in the concentration range 0.10 ≤x ≤ 0.40. Lattice parameters offcc phase of Y₂O₃ doped samples were calculated from the X-ray diffraction data. The lattice constant ‘a’ gradually decreases with increasing content of dopant concentration (x) for the Y₂O₃ doped system and obeys Vegard’s rule. The unit cell parameters for the (Bi₂O₃)_1−x (Gd₂O₃)_x doped samples showing rhombohedral phase were obtained on hexagonal setting.     

New rutile solid solutions,Ti1−4xLixM3xO2: M = Nb,Ta, Sb

Three extensive new rutile solid solution series have been prepared in which Ti⁴⁺ is replaced by a combination of Li⁺ and a pentavalent cation: Nb⁵⁺, Ta⁵⁺, Sb⁵⁺. The formulae are Ti_1?4xLi_xM_3xO₂: 0 < x ? 0.15, M = Ta; 0 < x ? 0.17, M = Nb; 0 < x ? 0.12, M = Sb. The solid solutions were characterised by X-ray powder diffraction and density measurements. In addition to the rutile solid solutions, LiNb₃O₈ forms a limited range of solid solutions, Li_1?yNb_3?3yTi_4yO₈: 0 < y ? 0.06.     

Complete, reversible H/Li ion exchange reaction between rhombohedral LiMO3 and perovskite-type HMO3 (M=Nb, Ta)

We demonstrate for the first time the complete, reversible H⁺/Li⁺ ion exchange reaction between HMO₃ and LiMO₃ (M=Nb, Ta) using molten LiNO₃ at 320°C for 5 days. HMO₃ were prepared from LiMO₃ by ion exchange reactions using dilute HNO₃. The results reveal that both LiMO₃ prepared by normal solid state reaction between Li₂CO₃ and M₂O₅, and by ion exchanged from HMO₃ using molten LiNO₃ are isostructural. LiMO₃ prepared using HMO₃ yields nearly uniformly sized crystallites in contrast to those prepared by conventional solid state synthesis. The present method is simple and inexpensive compared to other methods of preparation of high purity LiMO₃ powders.     

Electron microscopy investigations of metal-support interaction effects in M/Y2O3 and M/ZrO2 thin films (M=Cu,Ni)

Model systems of the clean and pure oxides Y₂O₃ and ZrO₂, as well as Cu/Cu₂O and Ni/NiO particles embedded in the respective oxides have been used to study the reduction behavior of the oxides and the eventually associated metal-support interaction effects in oxide-supported systems. Particular emphasis has also been given to the influence of the phase transformation in ZrO₂-containing systems on metal-support interaction. Whereas Y₂O₃ has been found to be an outstandingly structurally and thermally stable oxide even upon reduction in hydrogen up to 1073 K, ZrO₂ was found to undergo a series of phase transformations from amorphous ZrO₂ to polycrystalline tetragonal ZrO₂ (∼673 K) and subsequently to monoclinic ZrO₂ (above 873 K). Both phase transformations were found to be basically dependent on gas partial pressure and annealing rate. However, substantial reduction of the oxides did not take place during the phase transformations. In turn, both Cu- and Ni-containing systems were not observed to be substantially affected by any (strong) metal-support interaction effects such as encapsulation by sub-stoichiometric oxides or reductive formation of intermetallic phases, at least up to temperatures of 1073 K. Equally, for the ZrO₂-containing systems, also the phase transformations occurring at elevated temperatures did not cause structural or thermo-chemical alterations of the Cu or Ni-particles. Differences in the metal-support interaction between Cu- and Ni-particles have only been obtained in the structural “reference” systems, that is, if supported on SiO₂. Whereas Cu/Cu₂O particles on SiO₂ are basically unaffected by the reductive treatment at elevated temperatures, a Ni₃Si₂ intermetallic phase is formed if SiO₂-supported Ni/NiO particles are treated in hydrogen at 673 K and above.     

Structural adaptability in the system Bi2O3  WO3 : Higher members of the homologous series Bi2WnO3n+3

The ultramicrostructure of phases with n = 1, 2 and 3 in the hypothetical series Bi₂W_nO_3n+3 has been investigated by high resolution electron microscopy and energy dispersive X-ray emission spectroscopy. For n = 1 and 2, well ordered phases with the predicted compositions have been obtained, but for n = 3, a severely disordered assemblage containing intergrowths of the two known structures and strips of the n = 3 member is produced. No evidence for ordered structures with n > 2 has yet been obtained.     

Des conducteurs ioniques pseudo-bidimensionnels: Li8MO6 (M = Zr,Sn), Li7LO6 (L = Nb,Ta) et Li6In2O6

The ionic conductivity of the pseudo-2D oxides Li₈MO₆ (M = Zr, Sn), Li₇LO₆ (L = Nb, Ta) and Li₆In₂O₆ has been measured and related to their structures. The ideal lattice consists of octahedral sheets [(Li₂M)O₆]_n, [(Li□L)O₆]_n or [(In₂□)O₆]_n of CdI₂-type, between which 6 Li⁺ ions are inserted with a tetrahedral environment. As expected from the structures the highest lithium mobility is observed for Li₇LO₆ phases and the smallest one for Li₈MO₆.     

High-Pressure Phase Transitions of M2O5(M = V, Nb, Ta) and Thermal Stability of New Polymorphs

The stability regions of various M₂O₅(M = V, Nb, Ta) polymorphs were studied by quenching samples from 600–1300°C at pressures in the range 5.0–8.0 GPa. Above 7.0 GPa, Nb₂O₅and Ta₂O₅were found to have a new polymorph (Zphase) in which the metal atoms are in sevenfold coordination. In addition, the samples contained the high-pressure polymorph B-M₂O₅ with the rutile-related structure. Differential thermal analysis at atmospheric pressure showed a weak, broad exotherm, indicating that the transformation of Z-M₂O₅into other phases begins at 100–150°C and reaches completion at 400°C in Nb₂O₅and 550°C in Ta₂O₅. At p 8.0 GPa and t> 750°C, a new high-pressure phase B-V₂O₅, isostructural with B-Nb₂O₅, was identified (a= 11.9640(6) Å, b= 4.6986(3) Å, c= 5.3249(3) Å, = 104.338(4)°, V= 290.01 ų, Z= 4, sp. gr. C2/c). At atmospheric pressure, B-V₂O₅transforms into -V₂O₅, with two strong exothermic peaks at 230 and 270°C. Experiments in the pressure range 5.0–8.0 GPa confirmed that the high-pressure phase -V₂O₅has a broad stability region.     

Preparation of Bi2O3SiO2 films by a rapid quenching technique and their crystallization process

Using a rapid quenching technique, Bi₂O₃SiO₂ films were prepared. The films of δ-Bi₂O₃ solid solution (ss) were obtained from the quenched melt containing 5 to 17% SiO₂. The films were transparent when the SiO₂ content was more than 10%. In the films with the composition from 20 to 35% SiO₂, δ-6Bi₂O₃·SiO₂ ss coexisted with glass phase, while glass films were obtained from the melt containing more than 40% SiO₂. The δ-phase in the films found to show the perfect grain-orientation, as the (111) were parallel to the film plane. The quenched films were annealed at various temperatures to investigate their crystallization process.     

液相沉淀法制备球状Bi2O3粉料

以金属铋为原料,溶解在硝酸中,配置成Bi(NO3)3溶液,用NH3-NH4HCO3作沉淀剂,调节pH值,制备Bi2O3粉料.通过控制反应温度、加料速度、反应时间以及加入适量的分散剂,制备得粒径为2～3μm、粒度分布均匀、分散性良好的超细球状Bi2O3粉料.用Bi2O3粉料制备的ZnO压敏电阻,具有压比低,方波冲击合格率高,性能一致等优点.     

Preparation and electrical properties of a monophasic ZrO2Y2O3Bi2O3 solid electrolyte

A preparation method is described of monophasic yttria stabilized zirconia doped with Bi₂O₃. This material is prepared from a homogeneous power which, after pressing, is sintered in a Bi₂O₃ atmosphere. The resulting ceramic has a composition of 0.78rO₂-0.206 YO_1.5-0.014BiO_1.5. The grain boundaries are enriched with bismuth. A relative density of 95% of the theoretical one is attained at a considerably lower temperature than the bismuth free sample. The electrical conductivities of the monophasic Bi doped and the Bi-free electrolyte material do not differ significantly.     

Studies on the system V3O5 /1b Ti3O5

The system (V_1?xTi_x)₃O₅ has been studied by means of X-ray powder photography, DTA and magnetic susceptibility measurements. A continuous series of solid solutions has been found for samples prepared at 1175 K, while samples prepared at 1275 K showed the solid solubility in the V₃O₅ end phase to be limited by $\text{x}\text{< 0.7}$ DTA studies have shown that the peak associated with the V₃O₅(low) /1b V₃O₅(high) transition disappears at $\text{x}\text{= 0.024}$. The DTA studies have also confirmed the existence of a phase transition in γ-Ti₃O₅ ($\text{x}\text{= 1}$) at 227 K.     

High-purity TeO2–WO3–(La2O3, Bi2O3) glasses for fiber-optics

TeO₂–WO₃, TeO₂–WO₃–La₂O₃ and TeO₂–WO₃–La₂O₃–Bi₂O₃ glasses were produced by high-purity oxides mixtures melting in crucibles of gold or platinum in purified oxygen atmosphere. The total content of Cu, Mn, Fe, Co and Ni impurities was not more than 0.1–2 ppm wt in glasses and below 0.1 ppm wt in the initial oxides. The hydroxyl groups absorption coefficients of the tellurite glasses at the maximum of the absorption band (λ ∼ 3 μm) lay in the region of 0.01–0.001 cm⁻¹. Stability to crystallization characterized by T_x − T_g = 150–190 °C was demonstrated for high purity 75TeO₂–25WO₃ glasses by DSC-measurements. There were no thermal effects of crystallization and crystallized phases fusion in case of La₂O₃-containing glasses.The optical absorption losses, measured by the laser calorimetry method at λ = 1.06, 1.56 and 1.97 μm, did not exceed 40–120 dB/km for glass samples. The multimode optical fibers with optical losses of 50–250 dB/km at 1.2–2.2 μm were produced from high-purity TeO₂–WO₃–(La₂O₃, Bi₂O₃) glasses.     

BiOCl/Bi2O3异质结复合光催化剂的制备和光催化性能研究

以五水硝酸铋、硝酸、氢氧化钠、盐酸为原料,用盐酸浸渍法制备了盐酸与氧化铋物质的量比分别为0.3∶1、0.5∶1、0.7∶1、1∶1的BiOCl/Bi2O3异质结新型复合光催化剂。用X射线衍射(XRD)、热重-差热分析(TG-DSC)和扫描电子显微镜(SEM)等手段对材料进行了表征。250 W高压汞灯照射下,用光催化降解罗丹明B反应来测试催化剂的光催化活性,结果表明BiOCl/Bi2O3复合光催化剂的性能明显优于单体Bi2O3。当盐酸与氧化铋物质的量比为0.7∶1时,BiOCl/Bi2O3催化剂的光催化活性最佳。最后研究了抑制剂对BiOCl/Bi2O3复合光催化剂降解罗丹明B的影响,发现三乙醇胺和碘化钾都有一定的抑制作用。     

Single crystals in the Bi2O3/1bMoO3 binary system: Growth and optical properties

Single crystals of Bi₂O₃·3MoO₃ and 3Bi₂O₃·2MoO₃ in the Bi₂O₃/1bMoO₃ binary system were grown by pulling from the melt. Single crystal Bi₂O₃·MoO₃ (Bi₂MoO₆), which is well known as Koechlinite, could not be grown successfully. A new compound 3Bi₂O₃·2MoO₃ was found to melt congruently and to be easily grown from the melt. It belongs to the monoclinic crystal system with space group C⁴_2h. Refractive indices of Bi₂O₃·3MoO₃ and 3Bi₂O₃·2MoO₃ were investigated.     

Preparation and crystal structure of a new bismuth vanadate, Bi3.33(VO4)2O2

Single crystals of a new bismuth vanadate, Bi_3.33(VO₄)₂O₂ was prepared by hydrothermal reaction using a hydrated sodium bismuthate, NaBiO₃·nH₂O as one of the starting compounds. The crystal structure was determined by using single crystal X-ray diffraction data. This compound crystallizes in the triclinic space group (#2) with a = 7.114(1), b = 7.844(2), c = 9.372(2) Å, α = 106.090(7), β = 94.468(7) and γ = 112.506(8)°, Z = 2 and the final R factors are R1 = 0.052 and wR2 = 0.14 for 2085 unique reflections. The crystal structure is composed by four bismuth atoms with the coordination number of 6 or 8 and two VO₄ tetrahedra, and one of four bismuth atoms is statistically distributed in the splitting sites with the distance of 0.83 Å. This compound exhibited photocatalytic behavior for decomposition of phenol under visible light irradiation and its activity was less than that of monoclinic BiVO₄.     

Synthesis of (Na2O,PbO)-Nb2O5, (Na2O,BaO)-Nb2O5, and (K2O,SrO)-Nb2O5 thin films using sol-gel method

Homogeneous pore-free Ba₂NaNb₅O₁₅, KSr₂Nb₅O₁₅, and 2·Na₂O-PbO-6·Nb₂O₅ thin films were fabricated on sapphire substrates using the sol-gel technique. By controlling the gelation and coating process, thickness of thin films fabricated was controllable from ~ 40 nm to ~ 10 μm. Synthesized thin films possessed highly preferred orientated microstructure. Another advantage of this method is the subsequent heat treatment temperature dramatically decreased compared with other methods. This increases stoichiometry control and makes the large scale fabrication more feasible and efficient.