Unusual defects and the electronic structure of the nonstoichiometric perovskite SrFeO3-δ: a numerical approach

Abstract

In this article, we present a numerical attempt to model the microscopic and electronic structure of the oxygen-deficient perovskite SrFeO_3-δ in the cubic high-temperature phase. Within a classical Monte Carlo simulation, vacancies exhibit a linear Fe(III)–vac–Fe(III) configuration, an extended defect that can be described as a quadrupolaron. With reference to this defect we discuss the broad range of stability of the perovskite and the possible absence of small polaron hopping. The electronic structure is described by a simple tight-binding model, which is extended by considering the on-site spin pairing energy. Regardless of the concentration of oxygen vacancies δ, the Fermi level lies at the top of a σ* band with a strong contribution from oxygen 2p atomic orbitals. The conductivity is discussed as a function of δ considering the density of states and the degree of localization of eigenfunctions at the Fermi level.