Oxygen surface exchange and diffusion in LaGaO 3 based perovskite type oxides

Abstract

Isotopic exchange was used to determine the oxygen tracer diffusion coefficient and surface exchange coefficient of LaGaO 3 based perovskites at a temperature from 923 to 1173 K. The oxygen diffusion coefficient was found to be higher than the surface exchange coefficient. In addition, the change in activation energy of the surface exchange coefficient was also observed at 973 K. The results indicate that the oxygen exchange behavior of acceptor doped LaGaO 3 is similar to that of other oxygen ion conductors such as ZrO 2-Y 2O 3 and CeO 2-Gd 2O 3, rather than that was found for the isostructural, but mainly mixed conducting, perovskite oxides. It was noted that the diffusion coefficient was not influenced while the surface exchange coefficient was strongly affected by the oxygen partial pressure of isotopic exchange and the empirical relation was found to be a power of 0.45. Oxygen tracer diffusion data obtained by SIMS was compared to that obtained by the measurement of the electrical conductivity with the Nernst-Einstein relationship. For the temperatures at which the measurements were taken, the two were almost identical within the accuracy of SIMS, strongly indicating that the conductivity in LSGM is ionic. The high oxide ion conductivity in LSGM results from the high mobility of oxygen vacancies in addition to the high concentration of oxygen vacancies.