The anodic oxidation of Ti was used to produce layers of TiO2 which consisted of anatase or rutile or both. The anatase phase was formed at lower anodization potentials, while formation of the rutile phase began at potentials above 100V, due to electrical breakdown. Defects with a broad optical absorption in the infra-red range were generated only in anodic TiO2 layers, with co-existing anatase and rutile phases, under ultra-violet illumination in a water-containing atmosphere. These defects partially disappeared upon annealing at about 400C for 0.5h. A reversible defect reaction took place, in the surface regions, between the anatase and rutile phases.

Infrared-Active Defects in a TiO2 Mixture of Coexisting Anatase and Rutile Phases. Skryshevskyy, V.A., Dittrich, T., Rappich, J.: Physica Status Solidi A, 2003, 201[1], 157-61