Atomistic simulations of oxide ion diffusion in heavily doped lanthanum cobaltite

Molecular dynamics simulations of perovskite-structured LaCoO3 doped with alkaline earth and transition metal elements have been performed to provide a theoretical assessment of the relationship between oxide ion conductivity and composition in this system. Conductivities for compositions La1−xSrxCo1−yFeyO3−δ (0.8 < x < 0.9, 0 < y < 1.0) at 1500 °C are reported. Several compositions are simulated at other temperatures in order to estimate the activation energies for ionic conductivity. Conductivity is found to increase with increasing strontium content, but exhibits a minimum for iron contents of 50% irrespective of the strontium content. Although substitution of Co2+ ions for Co3+ ions increases the volume fraction of oxide ion vacancies, the ionic conductivity decreases as a result of strong interactions between the lower valency dopants and vacancies.