First-principles study of oxygen-deficient LaNiO3 structures

We describe the results of first-principles calculations of the properties of oxygen vacancies in LaNiO3. We consider isolated oxygen vacancies, pairs of vacancies, and vacancies at finite concentrations that form oxygen-deficient phases of LaNiO3. The key electronic structure question we address is whether and to what extent an oxygen vacancy acts as an electron donor to the Fermi level (mobile and conducting electronic states). More generally, we describe how one can quantify, based on electronic structure calculations, the extent to which a localized point defect in a metallic system donates electrons to the Fermi level compared to trapping electrons in localized defect states. For LaNiO3, we find that an oxygen vacancy does not create mobile carriers but instead makes the two Ni sites adjacent to it turn into Ni2+ cations. Energetically, we compute the formation energy and diffusion barrier for oxygen vacancies. Structurally, we show that pairs of vacancies prefer to form on opposite sides of a Ni cation, aligning along a pseudocubic axis. For finite concentrations of vacancies, we compute the dependence of the LaNiO3 lattice parameters on the vacancy concentration to provide reliable data for experimental determination of the oxygen content in LaNiO3 and LaNiO3 thin films.