Effect of epitaxial strain on cation and anion vacancy formation in MnO

Biaxial strain in coherent epitaxial thin films can have a pronounced effect on the point-defect profile in the films' material. Detailed fundamental knowledge of the interaction of strain with point defects is crucial to understanding the stoichiometry and resulting properties of strained thin films. Here we investigate the effect of biaxial strain on the formation energy of cation and anion vacancies using MnO as a model system. Our density-functional-theory calculations show that, as expected from local volume arguments, compressive strain favors the formation of cation vacancies. Interestingly, we find that small compressive and tensile strains lead to ordering of the resulting holes along the in-plane and normal direction, respectively, which should manifest in different anisotropic properties in the two strain states.