Oxygen Ion Migration in Perovskite-Type Oxides

Computer simulation techniques have been applied to perovskite-structured LaBO3 (where B = Cr, Mn, Fe, Co) in order to elucidate the mechanistic features and energetics of oxygen ion migration. For the four compounds considered, a common set of interatomic potentials was derived that correctly reproduces their observed cubic structures. The results support models in which diffusion is mediated by oxygen ion vacancies. Analysis of the potential energy surface demonstrates that vacancy migration takes place along the union octahedron edge, although not in a linear fashion but via a curved path. The calculated migration energies vary from 0.5 to 0.9 eV and are in accord with the available experimental values. We consider the relationship between the cation size and the migration energy, which was investigated by modifying the interatomic potential function to relate ionic radii directly to the short-range repulsive term. We also examine the energies of solution for alkaline-earth dopants on the La site with oxygen vacancy compensation. Ion size effects are found to be important, with Sr calculated to have the highest solubility. Finally, we investigate the formation of dopant-vacancy pair clusters.