The structural energetics and diffusion mechanisms of the two most important point defects in rutile TiO2, the oxygen vacancy (VO) and the titanium interstitial (TiI), were examined using the ab initio pseudopotential total-energy method. The two defects were found to be somewhat competitive in energy, with VO being more favorable in a larger range of the stoichiometry. The TiI, on the other hand, was shown to be the major diffusive species, since its low migration barrier was significantly smaller (by ∼1eV) compared to that of VO. The diffusion mechanisms of TiI parallel and perpendicular to the crystal c axis were found to be different with a surprisingly larger barrier along the more open [001] direction, which was originally thought to be the easier channel for Ti self-diffusion. These theoretical findings were in excellent quantitative agreement with existing experimental data.

Diffusion Mechanisms of Native Point Defects in Rutile TiO2: ab initio Total-Energy Calculations. Iddir, H., Öğüt, S., Zapol, P., Browning, N.D.: Physical Review B, 2007, 75[7], 073203