Ab Initio Investigation of Oxygen Ion Diffusion in the Layered Perovskite System YSr₂Cu₂FeO_7+δ (0 < δ < 1)

Extensive research on transition metal perovskite oxides as electrodes in solid oxide cells (SOC) has highlighted the potential ability of Fe-based perovskite oxides to catalyze oxygen reduction/evolution reactions (ORR/OER). The layered perovskite-type system YSr₂Cu₂FeO_7+δ has been reported to possess attractive electrocatalytic properties. This work applies density functional theory (DFT) calculations to investigate oxygen ion diffusion in the YSr₂Cu₂FeO_7+δ system. For δ = 0.5, it is found that in the most stable configuration, the oxygen vacancies in the FeO_1+δ plane are arranged to form Fe ions in tetrahedral, square pyramid, and octahedral coordination. Ab initio molecular dynamics (AIMD) simulations for YSr₂Cu₂FeO_7.5 (δ = 0.5) yield an oxygen ion diffusion coefficient of 1.28 × 10⁻⁷ cm²/s at 500 °C (Ea = 0.37 eV). Complementary results for YSr₂Cu₂FeO_7.2 (δ = 0.2) and YSr₂Cu₂FeO_7.75 (δ = 0.75) indicate that the oxygen diffusion occurs in the FeO_1+δ plane, and depends on the oxygen vacancies distribution around the Fe centers.