The present work derived defect disorder diagram representing the effect of oxygen activity on the concentration of both ionic and electronic defects for undoped TiO2. This diagram was determined using the equilibrium constants derived in the present work, including (i) the intrinsic electronic equilibrium constant, (ii) the equilibrium constant for the formation of oxygen vacancies, and (iii) equilibrium constant for the formation of titanium vacancies. These equilibrium constants are consistent with three properties determined independently, including: electrical conductivity, thermoelectric power and change of mass determined by thermogravimetry. The derived defect disorder diagram may be used for tailoring semiconducting properties of TiO2 that are desired for specific applications through the selection of optimized processing conditions.

Measurements of both electrical conductivity and thermoelectric power were used to monitor the equilibration kinetics of undoped single-crystal TiO(2) during prolonged oxidation at 1123 and 1323 K and p(O(2)) = 75 kPa. Two kinetics regimes were revealed: kinetics regime I (rapid kinetics), which is rate-controlled by the transport of oxygen vacancies, and kinetics regime II (slow kinetics), which is rate-controlled by the transport of titanium vacancies. The incorporation of titanium vacancies allows undoped p-type TiO(2) to be processed in a controlled manner. The kinetics data were used to determine the chemical diffusion coefficient (D(chem)) associated with the transport of titanium vacancies, which is equal to D(chem) = 8.9 x 10(-14) m(2) s(-1) and D(chem) = 9.3 x 10(-15) m(2) s(-1) at 1323 and 1123 K, respectively.

The equilibration kinetics of high-purity single-crystal TiO(2) were monitored using measurements of electrical conductivity in the temperature range 1073-1323 K and oxygen activity, p(O(2)), range 10(-13) to 75 kPa. The kinetics data were used to determine the chemical diffusion coefficient (D(chem)) within narrow ranges of p(O(2)). There was observed a complex effect of the p(O(2)) on the D(chem), which exhibits a maximum at the n-p transition. The effect of the p(O(2)) on the D(chem) was discussed in terms of the defect disorder and the related semiconducting properties. The activation energy of the D(chem), which also varies with the p(O(2)), exhibits a maximum at p(O(2)) = approximately 10(4) Pa (143 kJ/mol).