Hydrothermal stability of yttria- and ceria-doped tetragonal zirconia-alumina composites

Changes in the crystalline phase and microstructure resulting from hydrothermal ageing of Y-TZP, (Y,Ce)-TZP, Y-TZP-Al₂O₃ composites and (Y,Ce)-TZP-Al₂O₃ composites were investigated under hydrothermal conditions at 180 °C and 1 MPa. Although (Y,Ce)-TZP showed no tetragonal-to-monoclinic (tm) phase transformation during low-temperature ageing in air as compared with 3Y-TZP, the tetragonal phase of (Y,Ce)-TZP easily transformed to monoclinic phase by ageing under hydrothermal condition. This tm phase transformation invaded the inside of the body accompanied by microcracks. (Y,Ce)-TZP-Al₂O₃ composites were resistant to phase transformation during hydrothermal ageing.     

Varistor characteristics of vanadium oxide-doped zinc oxide ceramics modified with bismuth oxide

The effect of Bi₂O₃ on microstructure, electrical properties, dielectric characteristics, and aging behavior vanadium oxide-doped zinc oxide varistor ceramics was systematically investigated. Analysis of the phase indicated that the ceramics modified with Bi₂O₃ consisted of ZnO grain as a main phase and a few secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, BiVO₄, V₂O₅, and Mn-rich phase. The average grain size increased from 5.6 to 7.2 μm and the sintered density decreased in the range of 5.51–5.37 g/cm³ up to 0.05 mol%, whereas a further addition increased it to 5.40 g/cm³ at 0.25 mol%. The breakdown field decreased from 4,874 to 2,205 V/cm with an increase in the amount of Bi₂O₃. The ceramics added with 0.025 mol% Bi₂O₃ were characterized by a surprisingly high nonlinear coefficient (60) and very low leakage current density (20 μA/cm²). Bi atoms in the bulk acted as a donor to increase the electron concentration with an increase in the amount of Bi₂O₃.     

Investigation of phase stability and oxide ion performance in new perovskite-type bismuth vanadate

Samples of the BICDVOX system, formulated as Bi₄Cd_xV_2−xO_{11−(3x/2)−δ} in the Cd substitution range 0 ≤ x ≤ 0.25 were synthesized using the standard solid state reaction.The correlation between phase stability and oxide ion performance were investigated by variable temperature XRPD, DSC and AC impedance spectroscopy. The substitution of V⁵⁺ by Cd²⁺ exhibited different phase transitions upon varying composition. For compositions with x ≤ 0.05, two successive transitions; α↔β↔γ are evident, while the β↔γ transition exists in the composition range 0.05 < x < 0.175. However, some temperature dependent phenomena confirmed the exixtence of the γ′↔γ transition, coupled with the tetragonal symmetry stabilization for x ≥ 0.175. The maximum oxide ion conductivity at lower temperatures was observed for x = 0.20. It has also been found that the slow V⁴⁺ → V⁵⁺ re–oxidation results in increased defect trapping effects in the system at higher temperatures.     

Phase stability aspects of various apatite-aluminium oxide composites

For aluminium oxide-hydroxyapatite composites sintered in air, decomposition of hydroxyapatite to tricalcium phosphate was initiated at temperatures below 1000°C and completed at 1200°C. Composites of aluminium oxide and various apatites (hydroxyapatite, fluorapatite and chlorapatite) as well as the pure materials were hot isostatically pressed at 1200°C for 1 h at a pressure of 160 MPa. Due to the closed system used, the thermal stability was improved and no phase changes were detected in the hot isostatically pressed aluminium oxide-apatite composites. These materials were crushed and thereafter heat-treated in air at several temperatures in order to study the phase stability. In the fluorapatite and chlorapatite based composites, the apatite reacted with the moisture in the air and partly converted to oxyhydroxyapatite and decomposition of the latter phase was initiated. The phase composition in the materials was evaluated by X-ray powder diffraction and the microstructure of the hot isostatically pressed samples was studied in a scanning electron microscope.     

Interaction of zinc oxide with bismuth oxide

The lattice parameters of polycrystalline ZnO in mixtures of ZnO-Bi₂O₃ and their dependence on Bi₂O₃-concentration were determined. Simultaneously the influence of ZnO presence on the origin of various modifications of Bi₂O₃ was observed. On the grounds of the measured decrease of the elementary cell volume the supposition about the interaction of Zn-intersititals with overstoichiometric oxygen atoms in Bi₂O₃ was accepted. In accordance with this idea the changes of free carrier concentration of samples ZnO+5 mol% Bi₂O₃ in the dependence on annealing temperature were found.     

Determination of the purity of bismuth and bismuth oxide by atomic absorption spectrometry

To enable high-speed analyses in the preparation of high-purity bismuth and bismuth oxide, we have developed an atomic absorption technique which ensures Ag, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Te detection limits in the range 2 × 10⁻⁷ to 2 × 10⁻⁵ wt %. The technique was used to assess the purity of bismuth and bismuth oxide in metal refining and oxidation steps.     

氧化铋薄膜的制备及光催化性能研究

采用磁控溅射制备了氧化铋薄膜,研究了制备工艺对薄膜的结构、微观形貌和光学性能的影响,并对样品进行了光催化性能评价.结果表明,氧氩比和退火温度显著影响薄膜的性能.当氧氩比为20:80时获得的薄膜具有最佳光催化性能;随退火温度升高,薄膜结晶性增强,并逐渐出现Bi和Si的氧化物,经500℃退火的薄膜具有最强的光催化活性.     

Dielectric properties of vacuum-deposited bismuth oxide films

The dielectric properties of bismuth oxide films prepared by vacuum deposition have been studied in the frequency range 0.1–10 kHz and the temperature range 90–298.5 K. The capacitances C_p and C_s and the loss factor show dependences on the frequency, temperature and aging of the samples. The loss factor exhibits a flat maximum in its temperature variation curve at about 170 K. Interfacial polarization, which is caused by the excess bismuth and by various defects and impurities, is thought to be the main relaxation mechanism operating in the low frequency region.     

Ionic and electronic conductivities of yttria- and scandia-stabilized zirconia

We report a study and comparative analysis of the medium-temperature (850–1000°C) ionic and total conductivities of zirconia stabilized by yttriaand scandia-based mixed oxides. Zirconia stabilized by combined yttria- and scandia-based dopants is shown to have low electronic conductivity in a wide range of oxygen activities. Our data suggest the possibility of using the synthesized materials as membranes in intermediate temperature ceramic fuel cells.     

Phase separation in oxygen deficient gallium oxide films grown by pulsed-laser deposition

The oxygen pressure and the substrate temperature during pulsed-laser deposition play a major role on the nature and properties of gallium oxide films. At moderate substrate temperature (673 K) and under high vacuum (10⁻⁷ mbar) a nanocomposite film composed of Ga metallic clusters embedded in a stoichiometric Ga₂O₃ matrix may be obtained without postdeposition annealing. The growth of such films is due to a phase separation of largely oxygen deficient metastable gallium oxide films Ga₂O_x (x = 2.3) into the most stable phases (Ga and Ga₂O₃) and occurs for particular growth conditions. The composition and the surface morphology of films as well as their electrical behaviour are interpreted according to the effects of the parameters governing this phase separation (oxygen deficiency and temperature). It is suggested that the initial step in the disproportionation reaction is the formation of stoichiometric Ga₂O₃ nanocrystallites in the metastable sub-oxide Ga₂O_x phase. The crystallization of such nanosize particles is governed by the local distribution of oxygen and gallium species impinging the substrate during the growth and allowing nucleation centre with the Ga₂O₃ composition.     

The composition of crystals of bismuth silicon oxide

Crystals of Bi _x SiO_1.5x+2 with x ～ 12 can be pulled at rates of about 5 mm h^?1 from platinum crucibles in oxidizing atmospheres. Melts with x in the range 10 < x < 15 give crystals in which the range of x is only from x = 11.77± 0.03 to x = 12.05 ± 0.10. As a function of melt composition, the solid composition shows a minimum and a maximum. Growth from melts giving either extreme, results in crystals having a constant composition.     

Characterization of bismuth lead oxide by vibrational spectroscopy

Bismuth lead oxide is a promising fast-ion conductor, with an oxygen ion conductivity in excess of 1 S cm⁻¹ at 590 °C. The characterization of the system (Bi₂O₃)_1−x (PbO) _x has previously been investigated using powder X-ray diffractometry; however, a detailed study using vibrational spectroscopy has not been carried out. This work examines the phases present between x=0 and 1 using both infrared and Raman spectroscopy. Detailed spectra of the phases are included, as well as an analysis of those phases. In general, the phases are reasonably consistent with previously published data; however, certain aspects differ. γ-Bi₁₂PbO₁₉, for example, was found to be a solid solution stable over a wide range of PbO, rather than a single phase as previously published. A summary of the room-temperature phases, after having been quenched from specific temperatures, is included in the form of a proposed phase diagram.     

Spray pyrolysed bismuth oxide thin films and their characterization

Uniform, adherent and reproducible bismuth oxide thin films have been deposited on glass substrates from aqueous Bi(NO₃)₃ solution, using the solution spray technique. Their structural, surface morphological, optical, and electrical properties were investigated by XRD, AFM, optical absorption, electrical resistivity and thermo-emf measurements. The structural analysis from XRD pattern showed the formation of mixed phases of monoclinic Bi₂O₃ (predominant), tetragonal β-Bi₂O₃ and nonstiochiometric Bi₂O_2.33. The surface morphological studies on atomic force micrographs revealed round grain morphology of bismuth oxide crystallites. The optical studies showed a direct band gap of 2.90 eV for as-prepared bismuth oxide films. The electrical resistivity measurements of bismuth oxide films indicated a semiconducting behavior with the room temperature electrical resistivity of the order of 10⁷ Ω cm. From thermo-emf measurements, the electrical conductivity was found to be of n-type.     

Electrical transport properties of layered structure bismuth oxide: Ba0.5Sr0.5Bi2V2O9

The layered structure bismuth oxide, Ba_0.5Sr_0.5Bi₂V₂O₉, was prepared using solid state reaction technique. Room temperature X-ray diffraction study confirms the formation of the material with an orthorhombic crystal structure. The temperature dependent impedance parameters were investigated using an impedance analyzer in a wide range of frequencies (10²–10⁶ Hz) at different temperatures. The Nyquist plots reveal the presence of both grain and grain boundary effect above 275 °C. The bulk resistance of the material decreases with rise in temperature which shows negative temperature coefficient resistance behavior like semiconductor. The variation of ac electrical conductivity (σ_ac) was measured, and the activation energy of the material found to be 0.36, 0.33, 0.34, 0.31 eV at 10, 50, 100 and 500 kHz respectively. Ac conductivity data were used to evaluate the density of states at Fermi level. From the dynamic light scattering and electrophoretic light scattering study, it is observed that the particle show excellent aqueous dispersion stability without any change in hydrodynamic size and zeta potential.     

Studies of the electrical properties of bismuth oxide films

A detailed study has been made of the resistivity , activation energy ΔE, Hall coefficient R_H, mobility μ, thermoelectric power and TCR of vacuum-deposited films of bismuth oxide evaporated from silica and molybdenum boats in the temperature range 78°–525°K. The electrical parameters of these films differed considerably from those of oxidized films and this difference has been attributed to the dissociation of the bismuth oxide and the formation of intermediate products.