Oxygen Point Defect Chemistry in Ruddlesden-Popper Oxides (La$_{1-x}$Sr$_{x}$)$_{2}$MO$_{4{\pm}{\delta}}$ (M = Co, Ni, Cu)

TL;DR

This study uses density functional theory to analyze how oxygen point defects in Ruddlesden-Popper oxides vary with composition, revealing defect stability trends and a key electronic descriptor for their formation energies.

Contribution

It provides a detailed understanding of defect chemistry in Ruddlesden-Popper oxides, highlighting the role of electronic structure and composition in defect stability.

Findings

Peroxide interstitials become more stable with higher Sr content and transition metal atomic number.

O 2$p$-band center correlates linearly with defect formation energies.

Increasing defect concentration ({ extdelta}) destabilizes oxide interstitials and vacancies.

Abstract

Stability of oxygen point defects in Ruddlesden-Popper oxides (La$_{1-x}$Sr$_{x}$)$_{2}$MO$_{4{\pm}{\delta}}$ (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 ({\delta}). We demonstrate that the dominant O point defects can change between oxide interstitials, peroxide interstitials, and vacancies. Generally, increasing $x$ and atomic number of M stabilizes peroxide over oxide interstitials, as well as vacancies over both peroxide and oxide interstitials; increasing {\delta} destabilizes both oxide interstitials and vacancies, but affects little peroxide interstitials. We also demonstrate that the O 2$p$-band center is a powerful descriptor for these materials and correlates linearly with the formation energy of all the defects. The trends of formation energy versus $x$, M and {\delta} and the correlation with O 2$p$-band center are explained in terms of oxidation chemistry and electronic structure.