Comparative density functional theory study on the electronic and optical properties of BiMO4 (M = V, Nb, Ta)

By means of density functional theory computations, we investigated the electronic structures and optical properties of BiMO4 (M = V, Nb, Ta) in order to understand their different photocatalytic activities. BiNbO4 and BiTaO4 are direct band gap semiconductors, while BiVO4 has an indirect minimum band gap, and at the same time has two slightly larger direct band gaps. By comparing the relative ratio of effective mass, it was found that BiVO4 has not only superior mobility of carriers but also excellent separation of photoexcited electron-hole pairs in the [010] direction, which can be attributed to its layer-like structure and the preferred distribution of electrostatic potential. Because of the narrow band gap, superior mobility and separation of carriers, suitable redox potential and preeminent absorption in visible light, it is predicted that BiVO4 should have better photocatalytic activity as compared to BiNbO4 and BiTaO4.