Structural phase-dependent hole localization and transport in bismuth vanadate

We present theoretical evidence for the phase dependence of hole localization and transport in bismuth vanadate (BiVO₄). Our hybrid density-functional theory calculations predict that, in the tetragonal phase [tetragonal scheelite BiVO₄ ($ts$-BiVO₄)], an excess hole tends to localize around a BiO₈ polyhedron with strong lattice distortion, whereas, in the monoclinic phase [monoclinic scheelite BiVO₄ ($ms$-BiVO₄)], it spreads over many lattice sites. The phase-dependent behavior is likely related to the higher structural stability of $ms$-BiVO₄ than $ts$-BiVO₄, which may suppress hole-induced lattice distortions. Our study also demonstrates that the relatively weakly localized hole in $ms$-BiVO₄ undergoes faster diffusion compared to the case of $ts$-BiVO₄, irrespective of the fact that the degrees of localization and mobility vary depending on the choice of exchange-correlation functional. The mobility difference may provide an explanation for the enhanced photocatalytic activity of $ms$-BiVO₄ over $ts$-BiVO₄ for water oxidation, considering that the increased mobility would lead to an increase in the hole current to the catalyst surface.