Understanding Oxygen-Vacancy Migration in the Fluorite Oxide CeO₂: An Ab Initio Study of Impurity-Anion Migration

Abstract

The site exchange of an anion moiety (O, N, F, Ne, P, S, Cl, and Ar) with an oxygen vacancy in fluorite-structured CeO2 was studied by means of density functional theory (DFT) calculations. The obtained activation energies of migration vary between 0.2 and 0.9 eV, and increase with the formal valence of the migrating ion; the size of the migrating ion appears to play a minor role. An analysis of ion displacements suggests that repulsive Coulombic interactions between the migrating anion and oxygen ions as the next-nearest neighbors in the saddle-point configuration provide the dominant contribution to the activation energy of migration. As well as emphasizing the ease with which anion moieties are mobile in AO2 fluorite materials, these results suggest a new paradigm for understanding fast oxygen-ion conducting materials.