The O and cation diffusion processes in O ion conductors were considered. While the high O diffusivity determined the proper O ion conductivity, slow cation diffusion processes were important in sintering and degradation processes. Here, an analytical model was first considered for the ionic conductivity of a strongly acceptor-doped fluorite-type O-ion conductor: a concentrated solution of AO2  and B2O3. The model could be applied to yttria-doped zirconia and provided a qualitative explanation of the observed maximum in the conductivity as a function of the dopant fraction. The model considered nearest-neighbor interactions between O vacancies and dopant cations, which could be negligible, attractive or repulsive, and jump barriers that depended upon the nature of the cation-cation edge that had to be crossed during a jump between adjacent O sites. Cation diffusion processes in doped lanthanum gallates were then considered. The experimental results of nearly identical cation diffusion coefficients in the A- and B-sublattices of the perovskite could be explained by a bound defect cluster mechanism involving cation vacancies of both the A- and the B- sublattices and anion vacancies.

Oxygen and Cation Diffusion Processes in Oxygen Ion Conductors. M.Martin: Diffusion Fundamentals, 2007, 6[3], 39.1