The defect chemistry of TiO2 within the n–p transition regime was described. Quantitative considerations of the relationships between the concentration of ionic and electronic defects at the minimum of electrical conductivity vs. O partial pressure resulted in the derivation of a theoretical model. The model was based upon the empirical data on electrical conductivity for Cr-doped TiO2 (exhibiting n–p transition). This model was then applied to the determination of the intrinsic electronic equilibrium constant. Good agreement between this equilibrium constant and the experimental data on electrical conductivity for TiO2 doped with donors (Cr) was revealed. It was observed that the concentration of O vacancies determined by using the derived model was only slightly dependent upon the value of the electronic intrinsic equilibrium constant.

Defect Chemistry and Semiconducting Properties of Titanium Dioxide - I. Intrinsic Electronic Equilibrium. Bak, T., Nowotny, J., Rekas, M., Sorrell, C.C.: Journal of Physics and Chemistry of Solids, 2003, 64[7], 1043-56