Oxide ion conductivity in doubly doped PrGaO3 perovskite-type oxide

It was found that PrGaO3 doped with Sr (or Ca) for the Pr site and Mg for the Ga site exhibits the high oxide ion conduction which was slightly less than that measured for doubly doped La(Sr)Ga(Mg)O3 (LSGM). Doping alkaline earth cations for the Pr site and Mg for the Ga site of the PrGaO3 increased its oxide ion conductivity. For temperatures above 1073 K, the highest oxide ion conductivity was obtained for the composition Pr0.93Sr0.07Ga0.85Mg0.15O3 (PSGM). The apparent activation energy of Pr0.93Ca0.07Ga0.85Mg0.15O3 (PCGM) was as low as 0.65 eV. The electrical conductivity of PCGM was higher than that of LSGM at temperatures below 873 K. Although hole conduction was observed, electron conductivity of the doubly doped PrGaO3 was almost independent of the oxygen partial pressure from pO2 = 1 to 10 exp(-21) atm. It is clear that doped PrGaO3 is a new fast oxide ion conductor over a wide range of oxygen partial pressures. A nonlinearity was observed on the Arrhenius plot of electrical conductivity for Ca-doped PrGaO3 and the high temperature XRD measurement suggested that it was due to phase transition from orthorhombic to rhombohedral or tetragonal, which may decrease the mobility of oxide ions. Application of PSGM and PCGM for an electrolyte of solid oxide fuel cell was also investigated in order to cross-check the findings of the fast oxide ion conductivity. This study revealed that PSGM and PCGM were a new family of fast oxide ion conductors. 24 refs.