To obtain a greater insight into the mixed conduction mechanism of oxygen ions and electrons from atomistic and electronic level viewpoints, first-principles density functional theory (DFT + U method) was applied The results showed that oxygen vacancies strongly attracted localized electrons, forming associates between them. The migration energy of an oxygen vacancy in such an associate was substantially lowered compared to the unassociated case due to the simultaneous positional rearrangement of localized electrons during the ionic jump process. Accordingly, a concerted migration mechanism of oxygen vacancies and localized electrons in reduced ceria was proposed. This mechanism resulted in an increased diffusivity of oxygen vacancies, supported by localized electrons compared with that in pure oxide ion conductors.

A Concerted Migration Mechanism of Mixed Oxide Ion and Electron Conduction in Reduced Ceria Studied by First-Principles Density Functional Theory. M.Nakayama, H.Ohshima, M.Nogami, M.Martin: Physical Chemistry - Chemical Physics, 2012, 14[17], 6079-84