Exchange kinetics and diffusion of oxygen in systems based on lanthanum gallate

Abstract

The oxygen exchange and diffusion kinetics are studied by means of isotopic exchange in complex oxides La0.80Sr0.20Ga0.85 − x Mg0.15Co x O3 − δ (x = 0.00, 0.05, 0.15, 0.20, 0.25) and in electrolyte La0.88Sr0.12Ga0.82Mg0.18O3 − δ with gold-coated surface. The oxygen exchange rates and diffusion coefficients are determined in the bulk material and near the surface within the range of temperatures from 600 to 900°C and oxygen pressures from 0.3 to 1.0 kPa. The activation energies of the oxygen exchange and diffusion processes are calculated. By cobalt doping, gallium sublattice is shown to increase the interphase exchange rate; however, the oxygen transport properties in the bulk phase are not significantly affected by cobalt, while cobalt additive decreases the activation barrier of oxygen diffusion in the near-surface area. Gold activates the electrolyte surface, affecting the exchange rate and increasing the first-type exchange share. Cobalt substitution increases the third-type exchange share as compared to that of La0.88Sr0.12Ga0.82Mg0.18O3 − δ (x = 0.00, 0.05, 0.15, 0.20, 0.25) and in elec. The oxygen exchange with gas phase is assumed to be limited by molecular oxygen adsorption-desorption process on the electrolyte surface.