Trends in Surface Oxygen Formation Energy in Perovskite Oxides

Perovskite oxides comprise an important class of materials, and some of their applications depend on the surface reactivity characteristics. We calculated, using density functional theory, the surface O vacancy formation energy (E _Ovac) for perovskite-structure oxides, with a transition metal (Ti-Fe) as the B-site cation, to estimate the catalytic reactivity of perovskite oxides. The E _Ovac value correlated well with the band gap and bulk formation energy, which is a trend also found in other oxides. A low E _Ovac value, which is expected to result in higher catalytic activity via the Mars-van Krevelen mechanism, was found in metallic perovskites such as CaCoO₃, BaFeO₃, and SrFeO₃. On the other hand, titanates had high E _Ovac values, typically exceeding 4 eV/atom, suggesting that these materials are less reactive when O vacancy formation is involved in the reaction mechanism.