OXIDE ION CONDUCTIVITY IN DOPED NDALO3 PEROVSKITE-TYPE OXIDES

Oxide ion conductivity in doped NdAlO2 Perovskite-type oxides was investigated. Among the alkaline earth cations, the addition of Ca for Nd site is effective for increasing the oxide ion conductivity of NdAlO3. Oxide ion conductivity increased anomalously with increases in the amount of Ca, and attained the maximum at x = 0.1 in Nd1-xCaxAlO3, since the limit of the solid solution of Ca into the Nd site seems to be around x = 0.1. The addition of the cations for the Al site of Nd0.9Ca0.1AlO3 was also effective for increasing the oxide ion conductivity, and it was found that the substitution of Ga on Al sites is effective for enhancing the oxide ion conductivity of Nd0.9Ca0.1AlO3. The oxide ion conductivity increased with increasing the Ga content and the highest oxide ion conductivity was attained at x = 0.5 in Nd0.9Ca0.1Al1-xGaxO3. Since the increased oxygen ion conductivity by doping Ga suppressed the p-type semiconduction in high oxygen partial pressure range, electrical conductivity was almost independent of the oxygen partial pressure. The theoretical electromotive forces were obtained from the galvanic cell measurement where Nd0.9Ca0.1Al0.5Ga0.5O3 was used as the electrolyte. Furthermore, the fuel cell where Nd0.9Ca0.1Al0.5Ga0.5O3, Ni, and La0.6Sr0.4MnO3 were used as electrolyte, anode, and cathode, respectively, exhibited the short-circuit current density higher than 400 mA cm(-2) at 1273 K, when humidified H-2 and O-2 were used as fuels and oxidizing agent, respectively. These results suggest that the perovskite-type oxide, Nd0.9Ca0.1Al0.5Ga0.5O3, exhibits almost a pure oxide ion conductivity with high electrical conductivity over a wide range of oxygen partial pressures and temperatures.