Comparative studies of the kinetics of O interaction with undoped and Nb-doped thin films were carried out at temperatures ranging from 900 to 1300K. It was found that the equilibration time for undoped material was of the order of seconds. On the other hand, the equilibration time for Nb-doped material was of the order of several hours. The slow kinetics of the Nb-doped material indicated that the rate of equilibration was governed chemical diffusion. It was suggested that the motion of cation vacancies was responsible for bulk diffusion in Nb-doped material. The chemical diffusivity could be described by:

D(cm2/s) = 2.46 x 10-7exp[-167.3(kJ)/RT]

Chemical Diffusion in Nb-Doped TiO2. Radecka, M., Rekas, M.: Solid State Phenomena, 1995, 41, 121-8