First Principles Modeling of Oxygen Mobility in Perovskite SOFC Cathode and Oxygen Permeation Membrane Materials

Based on first principles DFT calculations, we analyze activation energies of oxygen vacancy migration in several complex ABO(3)-type perovskite candidate materials for SOFC cathodes and permeation membranes (La(Co,Fe)O3-delta (LCF) and (Ba,Sr)(Co,Fe)O3-delta (BSCF)). The atomic relaxation, charge redistribution and energies of the transition states of oxygen migration are compared to understand the microscopic origin of the exceptionally low migration barrier (high oxygen mobility) in BSCF. It is shown that the B-O distance is considerably shortened in the transition state for BSCF due to covalency of this chemical bond, which could be a reason for the significant reduction of the oxygen migration energy in this material. Additionally, the Goldschmidt tolerance factor based on Shannon ionic radii is revisited.