Formation and migration of oxygen vacancies in La_1-xSr_xCo_1-yFe_yO_3-δ perovskites: Insight from ab initio calculations and comparison with Ba_1-xSr_xCo_1-yFe_yO_3-δ

The formation and migration of oxygen vacancies in the series of (La, Sr)(Co, Fe)O_3-δ perovskites, which can be used as mixed conducting SOFC cathode materials and oxygen permeation membranes, are explored in detail by means of first principles density functional calculations. Structure distortions, charge redistributions and transition state energies during the oxygen ion migration are obtained and analyzed. Both the overall chemical composition and vacancy formation energy are found to have only a small impact on the migration barrier; it is rather the local cation configuration which affects the barrier. The electron charge transfer from the migrating O ion towards the transition metal ion in the transition state is much smaller in (La, Sr)(Co, Fe)O_3-δ compared to (Ba, Sr)(Co, Fe)O_3-δ perovskites where such a charge transfer makes a significant contribution to the low migration barriers observed (in particular for high Ba and Co content).