Molybdenum defect complexes in bismuth vanadate

Abstract

Monoclinic bismuth vanadate (BiVO₄) is a promising n-type semiconductor for applications in sunlight-driven water splitting. Several studies have shown that its photocatalytic activity is greatly enhanced by high concentrations of Mo and W dopants. In the present work, we performed ab initio calculations to assess the most favorable relative position between pairs of Mo dopants in BiVO₄. Surprisingly, we verify that the lowest energy configuration for Mo_V pairwise defects in BiVO₄ occurs on nearest-neighbor sites, despite the higher electrostatic repulsion and larger strain on the crystal lattice. Similar results were observed for W_V defect pairs in W-doped BiVO₄. We show that the origin of this effect lies in a favorable hybridization between the atomic orbitals of the impurities that is only verified when they are closest to each other, resulting in an enthalpy gain that overcomes the repulsive components of the pair formation energy. As a consequence, Mo and/or W doped BiVO₄ are likely to present donor–donor defect complexes, which is an outcome that can be applied in experimental approaches for improving the photocatalytic activity of these metal oxides.