Effect of oxygen vacancies on intrinsic dielectric permittivity of strontium titanate ceramics

We prepared oxygen-deficient strontium titanate ceramics and measured the THz dielectric spectra to discuss the effect of oxygen vacancies on the intrinsic dielectric permittivity. In the presence of oxygen vacancies, the lattice volume of strontium titanate increased. First-principles calculation revealed that the expansion of the lattice originated from repulsion between the oxygen vacancies and cations, causing a decrease in the covalency of the Ti–O bonding. THz dielectric measurement using a far-infrared spectroscopic ellipsometer made it clear that the Slater-type phonon mode hardened and then the intrinsic permittivity of strontium titanate decreased in the presence of oxygen vacancies.