Defects and Oxide Ion Migration in the Solid Oxide Fuel Cell Cathode Material LaFeO3

LaFeO3, a mixed ionic electronic conductor, is a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). Key to understanding the electronic and ion conducting properties is the role of defects. In this study ab initio and static lattice methods have been employed to calculate formation energies of the full range of intrinsic defects-vacancies, interstitials, and antisite defects-under oxygen rich and oxygen poor conditions, to establish which, if any, are likely to occur and the effect these will have on the properties of the material. Under oxygen rich conditions, we find that the defect chemistry favors p-type conductivity, in excellent agreement with experiment, but contrary to previous studies, we find that cation vacancies play a crucial role. In oxygen poor conditions O2- vacancies dominate, leading to n-type conductivity. Finally, static lattice methods and density functional theory were used to calculate activation energies of oxide ion migration through this material. Three pathways were investigated between the two inequivalent oxygen sites, O1 and O2; O2-O2, O1-O2, and O1-O1, with O2-O2 giving the lowest activation energy of 0.58 eV, agreeing well with experimental results and previous computational studies.