Equilibration Kinetics and Chemical Diffusion of Indium-Doped TiO2

The present work reports the gas/solid equilibration kinetics for In-doped TiO2 (0.4 atom % In) at elevated temperatures (1023-1273 K) in the gas phase of controlled oxygen activity [10(-13) Pa < p(O2) < 10(5) Pa]. Thus, the determined chemical diffusion coefficient is considered in terms of a microdiffusion coefficient that is reflective of the transport kinetics within very narrow ranges of oxygen activities. In analogy to pure TiO2, the chemical diffusion coefficient for In-doped TiO2 exhibits a maximum at the n-p transition point. The activation energy of the chemical diffusion exhibits a decrease with temperature from 200 kJ/mol at 1023 K to an insignificant value at 1273 K. This effect is reflective of a segregation-induced electrical potential barrier blocking the transport of defects. The absolute value of the chemical diffusion coefficient for In-doped TiO2 is larger from that of pure TiO2 by a factor of approximately 10. The effect of indium on the diffusion rate is considered in terms of the associated concentration of oxygen vacancies, which are formed in order to satisfy the charge neutrality for In-doped TiO2.