Oxygen Point Defect Chemistry in Ruddlesden–Popper Oxides (La[subscript 1–x]Sr[subscript x])[subscript 2]MO[subscript 4±δ](M = Co, Ni, Cu)

Abstract

Stability of oxygen point defects in Ruddlesden–Popper oxides (La[subscript 1–x]Sr[subscript x])[subscript 2]MO[subscript 4±δ](M = Co, Ni, Cu) is studied with density functional theory calculations to determine their stable sites, charge states, and energetics as functions of Sr content (x), transition metal (M), and defect concentration (δ). We demonstrate that the dominant O point defects can change between oxide interstitials, peroxide interstitials, and vacancies. In general, increasing x and atomic number of M stabilizes peroxide over oxide interstitials as well as vacancies over both peroxide and oxide interstitials; increasing δ destabilizes both oxide interstitials and vacancies but barely affects peroxide interstitials. We also demonstrate that the O 2p-band center is a powerful descriptor for these materials and correlates linearly with the formation energy of all defects. The trends of formation energy versus x, M, and δ and the correlation with O 2p-band center are explained in terms of oxidation chemistry and electronic structure.