The influences of external strain upon the diffusion properties of the bulk and sub-surface oxygen vacancy in rutile were systematically studied using first-principles calculations. For oxygen vacancies in the bulk, it was found that tensile (compressive) strain applied in the [001] direction or isotropically applied in the equivalent [110] and [1¯10] directions reduced (increased) the energy barriers of diffusion. Anisotropic strain applied in [110] and [1¯10] increased the energy barriers of diffusion in the two directions. Meanwhile it resulted in anisotropic diffusion behaviors. Between [110] and [1¯10], the bulk oxygen vacancy preferred to diffuse along the one in which more compressive or less tensile strain was applied. From sub-surface to surface, the most energetically favorable oxygen vacancy pathway was along the [110] rows terminated with the surface bridging oxygen atoms. The diffusion barrier of the oxygen vacancy in the first trilayer was much lower than that of a bulk oxygen vacancy. External in-plane tensile strain could further reduce the energy barrier of the sub-surface oxygen vacancy diffusion, and thus help to improve the diffusion of oxygen vacancies from bulk to surface.

Strain Effect on Diffusion Properties of Oxygen Vacancies in Bulk and Subsurface of Rutile TiO2. Wang, Z.W., Shu, D.J., Wang, M., Ming, N.B.: Surface Science, 2012, 606[3-4], 186-91