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 CaCoO 3 , BaFeO 3 , and SrFeO 3 . 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.