Here, the O vacancy in WO3 was studied by using an ab initio pseudopotential method within the local density approximation. It was shown that with the charge state change of the vacancy, a strong lattice relaxation, swing from one to the other side of the un-relaxed position, was found for the nearest W ions, accompanied by large changes in the electronic structure of the vacancy. It was found that an O vacancy in WO3 gave rise to 3 types of defect states: a donor-like state near the fundamental band-gap, derived from the top valence bands, a hyper-deep resonant state in the valence band and a high-lying resonant state in the conduction band, derived from the oxygen 2s bonding and anti-bonding band, respectively. The existence of the donor-like defect state offers a possible explanation for the dependence of the conductivity and the mid-gap absorption on the O deficiency.

Oxygen Vacancy in Cubic WO3 Studied by First-Principles Pseudopotential Calculation. S.Z.Karazhanov, Y.Zhang, A.Mascarenhas, S.Deb, L.W.Wang: Solid State Ionics, 2003, 165[1-4], 43-9