Structural Defects in W-Doped TiO₂ (101) Anatase Surface: Density Functional Study

Abstract

In this Article, the structural and electronic properties of the W-doped anatase (101) surface are investigated by first-principles density functional theory calculations. Several surface and subsurface substitutional positions are examined as well as the interaction of the W-dopant atoms with structural defects: cation vacant sites and additional oxygen atoms that are required to compensate the extra charge of the W⁶⁺ cations. It is found that the preferred configurations are those on which one W⁶⁺ cation and one Ti vacant site are first cationic neighbors with simultaneous formation of a wolframyl entity. The main mechanism of system stabilization is found to be based on the formation of wolframyl species that result from the close proximity, as first cationic neighbors of the W-dopant atom and the Ti vacant site. A second factor for system stabilization seems to be the separation of W⁶⁺ cations to reduce the energetic cost of the structural distortions introduced by the doping process. Results from molecular dynamics calculations indicate that W⁶⁺ cations have a 5 + 1 coordination with two W–O distances at 1.8 to 2.0 and 2.5 to 2.6 Å. All of these structural results are used to understand the experimental information available for W–Ti nanostructured oxides. The modifications introduced in the electronic structure of the anatase (101) surface by the doping process are discussed and rationalized. A comparative analysis of the density of states of doped and undoped slab models of this surface and a Bader charge analysis will be used to understand the electronic redistribution that takes place around the impurity atoms.