First-principles study of photoconductivity in BaTiO3 with oxygen vacancies

The photoconductivity of BaTiO2.5 with oxygen vacancy has been studied by the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The ground-state structure of BaTiO2.5 is obtained by minimization of the total energy. The partial densities of states show that the occupied states at the bottom of the conduction band have primarily Ti d orbital character. The photoconductivity shows that two novel features, in the low energy side, can be attributed to the intraband transition of free electronic carriers in the vicinity of the Fermi level and the interband transition of the Ti 3d(yz) related band states, to the Ti 3d(xy,xz) related band states, respectively. In addition, it is also found that the anisotropy of photoconductivity is enhanced because of the introduction of oxygen vacancy. The system can show the conductive behavior of electronic carriers, which is qualitatively in agreement with a recent experimental finding.