The oxide-ion conduction characteristics of doubly-doped material were investigated. It was found that samples which were doped with Sr or Ca on Pr sites and with Mg on Ca sites exhibited an oxide-ion conductivity which was slightly lower than that measured in doubly-doped La(Sr)Ga(Mg)O3. Doping with alkaline earth cations at the Pr sites and with Mg at the Ga sites of PrGaO3 increased its oxide-ion conductivity. At temperatures above 1073K, the highest oxide-ion conductivity was found for the composition: Pr0.93Sr0.07Ga0.85Mg0.15O3. On the other hand, the apparent activation energy of Pr0.93Ca0.07Ga0.85Mg0.15O3 was only 0.65eV. Therefore, the conductivity of Pr0.93Ca0.07Ga0.85Mg0.15O3 was higher than that of Pr0.93Sr0.07Ga0.85Mg0.15O3 at temperatures below 873K. Although hole conduction was observed, the electron conductivity of the doubly-doped material was almost independent of O partial pressures of between 1 and 10-21atm, and it was clear that the doped material was a new fast oxide-ion conductor over a wide range of O partial pressures. A non-linearity was observed in the Arrhenius conductivity plot for Ca-doped PrGaO3, and high-temperature X-ray diffraction data suggested that it was due to a phase transition from orthorhombic to rhombohedral or tetragonal. This could decrease the mobility of oxide ions.

Oxide Ion Conductivity in Doubly Doped PrGaO3 Perovskite-Type Oxide. T.Ishibara, H.Furutani, H.Arikawa, M.Honda, T.Akbay, Y.Takita: Journal of the Electrochemical Society, 1999, 146[5], 1643-9