Abstract
First-principles density-functional theory calculations in the generalized gradient approximation are carried out to study the relative stabilities of oxygen vacancies at surface and subsurface sites of anatase and , and, for comparison, of the prototypical rutile surface. Our results indicate that these defects are significantly more stable at subsurface than at surface sites in the case of anatase surfaces, whereas bridging oxygen sites are favored for O vacancies at rutile . Also, calculations of O-vacancy diffusion pathways at anatase show that the energy barrier to diffuse from surface-to-subsurface sites is sufficiently low to ensure a rapid equilibration of the vacancy distribution at typical surface annealing temperatures. These results could explain why, experimentally, anatase surfaces are found to have a significantly lower defect concentration and/or to be more difficult to reduce than those of rutile.
- Received 8 December 2008
DOI:https://doi.org/10.1103/PhysRevB.79.092101
©2009 American Physical Society