Doped LaGa03 exhibits high oxide ionic conductivity. Doping of Sr for the La site and Mg for the Ga site is the most effective method for enhancing the oxide ionic conductivity of LaGa03. The oxide ionic conductivity of Lao.9Sro.1Gao.8Mgo.2O3 was higher than that of Sc-doped Zr02 and slightly lower than that of Bi203 oxide. Furthermore, electronic or hole conduction was negligibly small in the oxygen partial pressure region from 1 to 10-20 atm.

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It was found for the first time that controlling the charge density in oxide semiconductors with an acceptor was effective for improving the activity to photolysis of H 2 O. Although the photodecomposition activity of NiO supported on nondoped KTaO 3 was negligibly small, doping small amount of acceptors such as tri-or tetravalent cations to KTaO 3 increased the formation rate of H 2 and O 2 . In particular, it was found that NiO supported on KTaO 3 doped with 8 mol % Zr 4+ exhibits higher activity to the photocatalytic decomposition of H 2 O than that of a well-known photocatalyst of Pt/TiO 2 .

An electrophoretic deposition (EPD) method was applied for the preparation of yttria‐stabilized zirconia (YSZ) films for solid oxide fuel cell (SOFC) applications. Dense YSZ films with uniform thickness can be readily prepared with the EPD method by using acetylacetone or acetone as a solvent. The open‐circuit voltages of SOFC, for which the YSZ films were prepared by the EPD method, increased with increasing repetitions of deposition and sintering. It was found that the open‐circuit voltage exceeded 1.0 V after five repetitions. When the planar SOFC was fabricated using La0.6Sr0.4MnO3 as a cathode, and electroless plating Pt as an anode, the open‐circuit voltage and the maximum power density attained were 1.03 V and 1.84 W·cm−2, respectively. Consequently, it became evident that the electrophoretic deposition was a suitable processing route for the formation of gas‐tight YSZ films with thickness less than 10 μm.

LaGaO,-based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this study, the stability of LaGaO,-based oxide was investigated. The LaGaO,-based oxide was found to be very stable in reducing, oxidizing, and CO2 atmospheres. Solid oxide fuel cells (SOFCs) using LaGaO,-based perovskite-type oxide as the electrolyte were studied for use in intermediate-temperature SOFCs. The power-generation characteristics of cells were strongly affected by the electrodes. Both Ni and LnCoO, (Ln:rare earth) were suitable for use as anode and cathode, respectively. Rare-earth cations in the Ln site of the Co-based perovskite cathode also had a significant effect on the power-generation characteristics. In particular a high power density could be attained in the temperature range 973-1273 K by using a doped SmCoO, for the cathode. Among the examined alkaline earth cations, Srdoped SmCoO, exhibits the smallest cathodic overpotential resulting in the highest power density. The electrical conductivity of SmCoO3 increased with increasing Sr doped into the Sm site and attained a maximum at Sm0 ,Sr,,CoO3. The cathodic overpotential and internal resistance of the cell exhibited almost the opposite dependence on the amount of doped Sr. Consequently, the power density of the cell was a maximum when Sm0 ,Sr,,CoO, was used as the cathode. For this cell, the maximum power density was as high as 0.58 W/cm2 at 1073 K, even though a 0.5 mm thick electrolyte was used. This study revealed that a LaGaO,-based oxide for electrolyte and a SmCoO,-based oxide for the cathode are promising components for SOFCs operating at intermediate temperature.