The self-diffusivity of O in TiO2-x was determined for x-values of between 0.0005 and 0.0084 by using gas/solid isotope exchange between 16O and 18O, and microgravimetric techniques. It was found that the diffusivity increased with increasing non-stoichiometry (table 7). It was concluded that O vacancies contributed about 20% to the non-stoichiometry at x = 0.0084. It was further suggested that both singly and doubly ionized vacancies were present in the approximate ratio of 1:2. The results indicated that a complete description of the defect structure should include interstitial Ti ions with 3 positive effective charges. These were the major defect in the more reduced oxide, while interstitial Ti ions with 4 effective charges became important in the almost stoichiometric material.

Oxygen Self-Diffusion in Non-Stoichiometric Rutile TiO2-x at High Temperature. Millot, F., Picard, C.: Solid State Ionics, 1988, 28-30, 1344-8