O/F-substitution in BiVO4: Defect structures, phase stability and optical properties

In a recent experimental study it has been shown, that fluorine-containing bismuth vanadate (F: BiVO4) reveals enhanced photoelectrochemical activity compared to pristine BiVO4. This work is a combined experimental and theoretical analysis of structural and electronic properties of F: BiVO4. A theoretical analysis of three different possible defect models for F: BiVO4 was carried out. The structures are optimized with the PBE + U method employing the GPAW program code. The most stable defect configuration corresponds to fluorine incorporation accompanied by the formation of cation vacancies, which is in good agreement with experimental results. The diffraction pattern of the calculated defect structure is compared to measured XRD data. Both, experiment and theory, predict a small band gap narrowing under O/F-substitution. For the measurements diffuse reflectron spectra were collected. Furthermore the influence of fluorine incorporation on the phase stability was investigated experimentally by high-temperature X-ray powder diffraction measurements at different temperatures and compared to theoretical results collected by DFT calculations. (C) 2017 Elsevier Masson SAS. All rights reserved.