The semiconducting properties of single-crystal TiO2 and their changes during prolonged oxidation at elevated temperatures and under controlled O activity were monitored using measurements of electrical conductivity and thermo-electric power. Two kinetic regimes were revealed: Regime I - rapid oxidation, associated with the transport of O vacancies, and Regime II - prolonged oxidation, which corresponded to the transport of Ti vacancies. The present data represent the first documented evidence for the formation and transport of Ti vacancies in TiO2. This finding allowed the processing of p-type TiO2 without the incorporation of aliovalent foreign ions.

Titanium Vacancies in Nonstoichiometric TiO2 Single Crystal. Nowotny, M.K., Bak, T., Nowotny, J., Sorrell, C.C.: Physica Status Solidi B, 2006, 242[11], R88-90