Defect chemistry and semiconducting properties of titanium dioxide: I. Intrinsic electronic equilibrium

The present work describes defect chemistry and semiconducting properties of TiO₂ within the n-p transition regime. Quantitative considerations on the relationships between the concentration of ionic and electronic defects at the minimum of electrical conductivity vs. oxygen partial pressure resulted in the derivation of a theoretical model. The model is based on the empirical data of electrical conductivity for Cr-doped TiO₂ (exhibiting n-p transition). This model was then applied for the determination of the intrinsic electronic equilibrium constant which is the following function of temperature:K_i = 3.74 × 10^-2exp[- 3.039 ± 0.053 eV/kT] A good agreement between this equilibrium constant and the experimental data of electrical conductivity for TiO₂ doped with donors (Cr) was revealed. It was observed that the concentration of oxygen vacancies determined using the derived model is only slightly dependent on the value of the electronic intrinsic equilibrium constant.