Here we consider the diffusion paths taken by Ti interstitials and O vacancies in bulk rutile TiO₂. While the diffusion of V_O on the TiO₂ (110) surface has been well studied with STM, its diffusion in the bulk is less well understood. Different oxygen ion diffusion mechanisms are considered by us, including O vacancy diffusion (site exchange) and oxygen interstitial migration. In addition, different Ti interstitial diffusion mechanisms are investigated. By using first-principles calculations, we have found that both V_O and Ti_i prefer to diffuse in an anisotropic manner in bulk rutile.

      In the case of oxygen vacancies, we find that the transition state through the edge of the Oh structure is preferable to a transition through the center of Oh structure. In the case of Ti interstitials, we find that the Ti interstitial prefers to diffuse via the 32c Oh site through open channels along [001] direction. This result is consistent with the previous interstitial diffusion experiments on rutile TiO₂. This discovery improves our understanding of intrinsic defect diffusion and will assist in the future exploration of extrinsic defect diffusion.