New cation interstitial defect models were derived for sub-stoichiometric rutile TiO2-x. These consisted of linear arrangements containing two face-shared octahedral pairs of trivalent cations. Diffusion mechanisms were described whereby these may readily aggregate to form pairs of crystallographic shear planes, as observed recently by high-resolution electron microscopy, when TiO2-x specimens were cooled relatively slowly from 1050C. Electrostatic arguments explain why these defects have very much lower formation and migration energies than the traditional ″point defect″ interstitial model.

Structure of Cation Interstitial Defects in Nonstoichiometric Rutile. Bursill, L.A., Blanchin, M.G.: Journal de Physique - Lettres, 1983, 44[4], 165-70