Electronic, optical, and photocatalytic properties of the wolframite InNbO4 and InTaO4 compounds

The first-principles calculations based on density functional theory (DFT) have been realized to study electronic, optical, and photocatalytic properties of the wolframite InNbO4 and InTaO4 compounds. In order to clarify the question of the valance-to-conduction bandgap of the pristine compounds, still debated in the literature, a series of recently developed exchange and correlation (XC) potentials have been employed, besides the standard generalized gradient approximation. It was concluded that the Becke-Johnson (BJ) potential has been the most successful, resulting in bandgap values of 3.71 eV and 4.20 eV for the InNbO4 and InTaO4 respectively, in agreement with recent experimental studies. By employing this XC potential, the electronic structure and optical properties of both compounds have been calculated and analyzed. A good agreement of the calculated reflectivity and absorption spectra with available experimental data assures that the DFT approach with BJ XC potential correctly describes the electronic properties of InNbO4 and InTaO4. Their photocatalytic efficiencies have been analyzed by calculating band-edge positions with respect to the H+/H2 reduction, and O2/H2O oxidation potential. It was concluded that both compounds exhibit band alignments suitable for efficient water splitting photocatalysis. However, due to their large bandgaps, the pristine materials should contain intrinsic and/or extrinsic defects to absorb in visible part of the solar spectrum.