Chemical diffusion in single crystals was studied at 1323K. It was found that, at this temperature, the chemical diffusivity for migration perpendicular to the c-axis was 3.4 times the chemical diffusivity parallel to the c-axis. This confirmed that, regardless of the deviation from stoichiometry in this material, the direct interstitial jump which strongly favored diffusion along the c-axis did not operate in the case of TiO2. This was contrary to observations of the heterodiffusion of small metallic ions.

Anisotropy of Ionic Transport Properties of Nonstoichiometric Single Crystals of Rutile TiO2-x at High Temperature. Millot, F.: Journal of Materials Science Letters, 1985, 4[7], 902-3