First principles calculations of oxygen vacancy formation and migration in Ba 1-xSr xCo 1-yFe yO 3-δ perovskites

Based on first principles DFT calculations, we analyze oxygen vacancy formation and migration energies as a function of chemical composition in complex multicomponent (Ba,Sr)(Co,Fe)O _3-δ perovskites which are candidate materials for SOFC cathodes and permeation membranes. The atomic relaxation, electronic charge redistribution and energies of the transition states of oxygen migration are compared for several perovskites to elucidate the atomistic reason for the exceptionally low migration barrier in Ba _0.5Sr _0.5Co _0.8Fe _0.2O _3-δ that was previously determined experimentally. The critical comparison of Ba _1-xSr _xCo _1-yFe _yO _3-δ perovskites with different cation compositions and arrangements shows that in addition to the geometric constraints the electronic structure plays a considerable role for the height of the oxygen migration barrier in these materials. These findings help understand advantages and limitations of the fast oxygen permeation and exchange properties of Ba _0.5Sr _0.5Co _0.8Fe _0.2O _3-δ.