First-Principles Calculations of Oxygen Vacancy Formation in Epitaxially Strained La1-xCaxMnO3
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Using epitaxial strain as a degree of freedom is a promising way to tailor the properties in thin films of transition metal oxides. Since the ground state of such materials tend to have many competing low-energy states they are susceptible to small perturbations, potentially inducing new phenomena. Due to the choice of different substrates and growth orientations, a wide range of strain can be applied in the thin films, giving researchers the ability to fine-tune the material properties. In this work, the effect of epitaxial strain on the oxygen vacancy formation ener- gies in different compositions of La1−xCaxMnO3 is calculated from first-principles within the DFT + U framework using the PBEsol functional. Due to the different spatial orientation of the Mn-O-bonds, it is possible to distinguish between two chemically inequivalent oxygen anions with a differing reponse to biaxial strain. This difference is reflected in the oxygen vacancy formation energies, which for all composition exhibit a different strain response. A displacement of oxygen anions towards the La/Ca-cations was found. For the intermediate compounds, the formation energies are largely influenced by which cation the oxygen is displaced towards. In combination with the reported phenomenon of surface segregation of cations, this could potentially be utilized in creating oxygen vacancy concentration gradients for use in novel electronics design.