High oxide ion conduction in sintered oxides of the system Bi2O3-WO3

The ionic conduction in sintered oxides of the system Bi₂O₃-WO₃ was investigated by measuring conductivities and ion transference numbers under various conditions. The ion transference number was measured by an oxygen concentration cell employing the specimen tablet as the electrolyte.It was found that a compound 3Bi₂O₃ WO₃ and its solid solution were high oxide ion conductors, the conductivities of which were about one order of magnitude higher than those of the well-known oxide ion conductors such as stabilized zirconias. In contrast to pure Bi₂O₃ which is a completely electronic conductor below 730°C, these materials showed high oxide ion conduction even below 700°C accompanied by little electronic conduction. 3Bi₂O₃ WO₃ has the face centered cubic structure, probably of the fluorite type, and the oxide ion conduction was thought to be attributed to the migration of oxide ion vacancies in the crystal.     

High oxide ion conduction in the sintered oxides of the system Bi2O3-Gd2O3

In order to characterize the conduction behaviour in the sintered oxides of the system Bi₂O₂-Gd₂O₃, the electrical conductivity in air and the emf of the oxygen concentration cell were measured. The new rhombohedral phase found in this system exhibited high oxide ion conduction especially at relatively high oxygen pressure. The rhombohedral phase was stable in the composition range between 10 and 30 mol% Gd₂O₃ below 600° C and was transformed into the face-centred cubic phase with rising temperature, the conduction in which was by oxide ion as in the rhombohedral phase. At concentrations greater than 35 mol% Gd₂O₃, the fcc phase was stable over a wide range of temperature (～900° C) and kept its high oxide ion conduction. The conductivities of rhombohedral (Bi₂O₃)_0.90(Gd₂O₃)_0.10 and fcc (Bi₂O₃)_0.65(Gd₂O₃) _0.35 ^* are 4.5 and 2.4×10^?2 cm^?1 at 600°C, respectively. These are about one order of magnitude higher than that of the well-known yttria-stabilized zirconia at corresponding temperatures. High-oxide ion-conduction in the rhombohedral and fcc phase was considered to be due to the appreciable numbers of oxide ion vacancies in these crystals.     

High oxygen ion conduction in sintered oxides of the Bi2O3-Er2O3 system

The phase diagram of the Bi₂O₃-Er₂O₃ system was investigated. A monophasic f c c structure was stabilized for samples containing 17.5–45.5 mol% Er₂O₃. Above and below this concentration range polyphasic regions appear. The f c c phase showed high oxygen ion conduction. The ionic transference number is equal to one for specimens containing 30 mol% Er₂O₃ or less, while an electronic component is introduced at low temperatures for specimens containing 40–60 mol% Er₂O₃. Between 673 K and 873 K a maximum in the conductivity was found at 20 mol% Er₂O₃. (Bi₂O₃)_0.8.(Er₂O₃)_0.20 is found to be the best oxygen ion conductor so far known. The conductivity at 773 K and 973 K is 2.3 ^–1m^–1 and 37 ^–1 m^–1 respectively. These values are 2–3 times higher than the best oxygen ion conductor reported for substituted Bi₂O₃ systems and 50–100 times higher than those of stabilized zirconia (ZrO₂)_0.915(Y₂O₃)_0.085 at corresponding temperatures.     

Oxide ion conduction in the sintered oxides of MoO3-doped Bi2O3

In order to examine the conduction behaviour in the sintered oxides of MoO₃-doped Bi₂O₃, the electrical conductivity in air and the EMF of oxygen gas concentration cell were measured with respect to the phase relation determined by X-ray diffraction.The tetragonal single phase oxide containing 22 mol% MoO₃ was found to be a high oxide ion conductor, the conductivity of which was comparable to those of stabilized zirconias. The partial electronic conduction in this phase was negligibly small at relatively high oxygen pressure. The oxide ion conduction was considered to be attributable to an appreciable amount of oxygen vacancies present in the crystal. In the monoclinic compound 3Bi₂O₃·2MoO₃, the oxide ion conduction was also observed. Although the conductivity of this phase was somewhat lower than that of the tetragonal phase, the activation energy for conduction (53·5 kJ mol^–1) was much lower than the values for usual oxide ion conductors.     

High oxide ion conduction in sintered Bi2O3 containing SrO,CaO or La2O3

Ionic conduction in sintered oxides of the system Bi₂O₃-SrO was investigated by measuring the conductivity and ion transference number under various conditions. The ion transference numbers were measured by an oxygen concentration cell employing the specimen as the electrolyte.It was found that the solid solution containing 2040 mole% SrO which had a rhombohedral structure was an almost pure oxide ion conductor under a relatively high partial pressure of oxygen, and that the conductivity was several times higher than that of stabilized zirconias at the same temperatures up to 800°C. Oxide ion conduction was confirmed also by quantitative determination of generated O₂ from the anode of the oxygen concentration cell during discharge.The sintered specimens of the systems Bi₂O₃-CaO and Bi₂O₃-La₂O₃ were found also to be oxide ion conductors, and the ion transference numbers were greater than 0.9.     

Oxide ion and electron mixed conduction in sintered oxides of the system Bi2O3-Pr6O11

Oxide ion and electron conduction in sintered oxides of the system Bi₂O₃-Pr₆O₁₁ have been studied. Two types of rhombohedral phase are formed in this system. Oxide ion conduction is predominant in the rhombohedral-phase present in the composition range less than 35 mol% Pr₂O_11/3. Electronic (hole) conduction appeared in addition to oxide ion conduction in another rhombohedral phase containing more than 40 mol% Pr₂O_11/3. This phase is of the LaOF-type which is a distorted defect fluoritetype structure. Electronic conduction in the LaOF-type phase is considered to be due to the change of oxidation state of praseodymium at high temperatures.     

Conduction in Bi2O3-based oxide ion conductors under low oxygen pressure. I. Current blackening of the Bi2O3-Y2O3 electrolyte

The cathodic current blackening of Bi₂O₃-based oxide ion conductors was examined for the Bi₂O₃-Y₂O₃ electrolyte at low oxygen pressure. In air, more than 500 mA cm^–2 d.c. could be passed at 600° C without causing changes in the electrolyte itself. However, in argon gas, a limiting current of 3 mA cm^–2 was observed and the electrolyte was blackened at the cathode side. The limiting current was ascribed to control by the diffusion of oxygen gas at the cathode. The blackened oxide was found to consist of a mixture of Bi metal and Bi₂O₃-Y₂O₃ solid solution and to exhibit the equilibrium oxygen partial pressure almost corresponding to that of the Bi, Bi₂O₃ mixture.     

Oxide/oxide composites in the system Cr2O3-Y2O3-Al2O3

Ceramic compacts in the systems Al₂O₃–Y₂O₃, Cr₂O₃–Y₂O₃ and Y₃(Cr_yAl_1-y)₅O₁₂ (Cr-doped YAG) were prepared by solid state reaction in calcined co-precipitated powder mixtures of appropriate compositions. Various solid-solution phases were formed, e.g. Y₃(Al_1-xCr_x)₅O₁₂, YAl_yCr_1-yO₃ and Al_2-xCr_xO₃. Composite materials in the pseudo-binary or ternary systems Al₂O₃–Y₃Al₅O₁₂, Cr₂O₃–Y₂O₃ and Y₃(Al_1–xCr_x)₅O₁₂–YAl_yCr_1–yO₃–(Al_zCr_1−z)₂O₃ were obtained by hot-pressing appropriate powder precursors at 1600–1650°C for 1 h. The microstructure of the prepared materials was studied in a scanning electron microscope with element analysis facilities. X-ray diffraction was used to reveal the phases present and their lattice parameters. The chemical compatibility of these phases was investigated. The results are discussed with a special emphasis on the solubility of Cr in the YAG structure, and on the compatibility relationship between Cr-doped YAG and its neighbouring phases. A gel-coating process for preparing Al₂O₃–YAG composites with tailored microstructures is also described.     

Oxide ion and electron mixed conduction in the fluorite-type cubic solid solution in the system Bi2O3-Tb2O3.5

Electrical conduction in sintered oxides of the system Bi₂O₃-Tb₂O_3.5 has been investigated. Oxide ion conduction was observed in the rhombohedral (low temperature) phase and the f c c (high temperature) phase present in the composition range less than 20mol% Tb₂O_3.5. The fcc phase could be stabilized at lower temperatures by adding more than 30 mol % Tb₂O_3.5. In addition to oxide ion conduction, appreciable electronic conduction appeared in this composition range. The oxide ion transport number of this phase decreased with increasing content of Tb₂O_3.5 and the specimens having 40–50 mol % Tb₂O_3.5 showed mixed conduction where electrical conduction was comparably contributed by oxide ions and electrons. Electronic conduction in the fee phase was considered to be due to the change in valence of terbium at high temperatures.     

Luminescence of oxide ceramics in the Bi2O3-Er2O3-CeO2 system

The method of pulse high-current cathode luminescence is used to study the Bi₂O₃-Er₂O₃-CeO₂ system at room temperature in air. New luminescence centers associated presumably with cation vacancies and an anion vacancy are determined in systems containing CeO₂. The luminescence parameters are shown to behave nonmonotonically with variation of the composition of the system. It is assumed that an abrupt change in these parameters at a certain composition of the substance corresponds to a phase transformation.     

A strong ceramic in the Al2O3-ZrO2-Y2O3 system

Conclusions A highly dense ceramic based on the eutectic composition of the Al₂O₃-ZrO₂ system was obtained using 3 mole % Y₂O₃ addition. The ceramic has a fine-grained structure and high hardness and strength.Translated from Ogneupory, No. 2, pp. 8–10, February, 1987.     

高韧性Nb2O3-Y2O3-ZrO2陶瓷的制备

采用Nb2O3、Y2O3复合稳定剂,制得了高韧性、高强度的四方相ZrO2陶瓷材料,发现在Y2O3－ZrO2材料中加入0．5－1molNb2O3,可使材料在保持原有抗弯强度的同时,一定程度上改善了断裂韧性和相组成。     

High ionic conduction in tetragonal solid solution of the system La2O3-MgF2

LaOF-type tetragonal solid solution was found in the system La₂O₃–MgF₂. This phase showed higher anionic conduction than the previously reported cubic solid solution in the system La₂O₃–CaF₂. Electrolysis by Tubandt's method showed that fluoride ion conduction was dominant in this solid solution. The fluoride ions were considered to be easily substituted by oxide ions through cathode reaction in the oxygen atmosphere.     

Phase equilibria in the Bi2O3-CuO-Nb2O5 ternary system

A complete subsolidus ternary phase diagram of the Bi₂O₃-CuO-Nb₂O₅ (BCN) system was constructed. Careful firing control and phase analysis were applied to determine the phase assemblages and compatibilities over a wide range of temperatures, i.e. 700–925 °C. Phase-pure BCN pyrochlores were found to crystallise in cubic symmetry, space group Fd3m, No. 227 with lattice constants in the range of 10.4855 (5)<x<10.5321 (3). The mechanism of this limited subsolidus series could be represented by a general formula, Bi_3.08−xCu_1.84+2x/9Nb_3.08+7x/9O_14.16+6x/9 (0≤x≤0.36) wherein the reduction in Bi content was compensated by a proportion amount of copper and niobium together with non-stoichiometry in oxygen.     

Film formation in the Bi2O3 — TiO2 — Fe2O3 ternary system

The processes of film formation in a ternary system are studied, beginning with the preparation of the working solution and up to coat firing. It is demonstrated that the properties and quality of a coating are determined at the stage of preparing a film-forming solution and depend on the size and shape of the sol particles, the film porosity, and the diffusion process at the glass-film interface.     

Microstructure and enhanced magnetic properties of low-temperature sintered LiZnTiMn ferrite ceramics with Bi2O3-Al2O3 additive

Bi₂O₃ and Al₂O₃ were proven to separately have an impact on grain growth of LiZn ferrite ceramics. In this study, we synthesized LiZnTiMn ferrite ceramics under low temperature (<920 °C) using rationally designed formula of Bi₂O₃-Al₂O₃ as sintering agents. Microstructures, densities, and ferromagnetic performances were systematically investigated. Results show that appropriate amount of Bi₂O₃-Al₂O₃ leads to successful sintering of LiZnTiMn ferrites even below 900 °C. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) results show that spinel structure ferrite ceramics were obtained and that the addition of Bi₂O₃-Al₂O₃ accelerated solid-state reaction. Corresponding ferromagnetic properties, including saturation induction (B_s), remanence square ratio, coercivity (H_c), ferromagnetic resonance linewidth (ΔH), and M_s, were also investigated. At 920 °C, with addition amount of x=1 wt%, we obtain excellent performance: B_s=306 mT, B_r/B_s=0.849, H_c=2.34Oe, and ΔH=275 Oe. Results indicate that Bi₂O₃-Al₂O₃ is promising sintering agent for low-temperature sintering of LiZnTiMn ferrite ceramics.