Difference in valence band top of BiVO4 with different crystal structure

The BiVO4 samples with different crystal forms were selectively synthesized by a coprecipitation route. The XRD and Raman spectra reveal that the samples were crystallized in tetragonal zircon type, tetragonal scheelite type and monoclinic scheelite type. The optical band gaps of BiVO4(t-z), BiVO4(t-s) and BiVO4(m-s) are 2.9, 2.6 and 2.45 eV, respectively. The valence-band XPS results indicate that the valence band (VB) top of BiVO4(t-s), BiVO4(t-z), and BiVO4(m-s) become more positive. The difference in band structure of BiVO4(m-s) and BiVO4(t-s) originates from the difference in the VB top.