Diffusion of oxygen vacancies on a strained rutile TiO2(110) surface

Based on first-principles calculations of the rutile TiO2(110) surface with different types of oxygen vacancies, a phase diagram is constructed for the energetically favorable oxygen vacancy as a function of the externally applied in-plane strain. When the strain is relatively small, the bridging oxygen vacancy (BOV) is the energetically favorable one. The pathways and the energy barriers of surface diffusion of the BOV under different external strain are studied. For the cross row diffusion of the BOV along [1 (1) over bar0], a concerted diffusion mechanism mediated by the in-plane oxygen vacancy is found to be energetically more favorable than the hopping diffusion. The energy barrier of the concerted diffusion along [1 (1) over bar0] and that of the hopping diffusion along [001] are found to decrease with increasing strain. The former decreases more dramatically than the latter when the strain is applied along [1 (1) over bar0], which suggests a possible way of facilitating the diffusion anisotropy.