Electronic Structure and Defect-Induced Properties of Oxygen-Deficient CaMnO _3−δ : Insights from First-Principles Calculations

Understanding the role of oxygen vacancies in perovskite oxides is essential for tailoring their functional properties. In this study, we employ density functional theory (DFT) calculations to investigate the structural, electronic, and defect-related properties of CaMnO3-δ across a wide range of oxygen vacancy concentrations. Although prior studies have examined oxygen vacancies in CaMnO3-δ, here we present a systematic investigation across the full range from δ = 0 to δ = 0.5 in increments of Δδ = 0.0625, thereby providing detailed new insights into its defect chemistry. Using cluster expansion techniques and high-accuracy relaxations, we identify ground-state configurations for each oxygen vacancy concentration and analyze their lattice distortions, bond length variations, and charge redistribution. Our results reveal a nonlinear progression of lattice parameters and bond environments with increasing oxygen vacancy concentration, accompanied by significant changes in the electronic band structure. Bader charge analysis indicates a progressive reduction in Mn oxidation state and charge compensation among all atomic species. As the estimated cost of creating oxygen vacancies increases at high concentration, from 2.03 to 2.26 eV, there exists a thermodynamic limit to vacancy incorporation at high oxygen vacancy concentrations. These findings provide a comprehensive understanding of how oxygen vacancies influence the stability and electronic behavior of CaMnO3-δ, offering insights relevant to its use in different types of applications.