First-principles study of oxygen vacancy formation in strained oxides

Based on first-principles density functional theory calculations and chemical bond analyses, we attempted to study the formation of oxygen vacancies (V-O) in strained Ti-based oxides. Structural features (e.g., cell volume and mean Ti-O bond length) exhibit a clear and linear correlation with strain. Further, electronic features (e.g., bandgap and Ti-O covalent bond strength) exhibit similar trends for hydrostatic, biaxial, and uniaxial strains, except for shear strains. We investigated the impact of strain on the formation of V-O and found that the formation energy in strained oxides was almost linearly linked to changes in the cell volume, bandgap, and Ti-O bond strength of the host oxide, where V-O were formed. However, these correlations are not valid in compressively strained systems, which include Ti-O bonds-the bond length being shorter than the sum of Ti and O ionic radii, and shear-strained systems.