The effects of sc doping and o vacancy on the electronic states and optical properties of m-bivo₄

Based on density functional theory (DFT), the effects of scandium (Sc) doping and oxygen vacancy (V_O ) on the electronic states and optical properties of monoclinic BiVO₄ (m-BiVO₄) are investigated. The generalized gradient approximation plus U (GGA+U) method is adopted during the calculation of the electronic properties to compensate for the limitations of the DFT method. The ideal m-BiVO₄ has a direct band gap of 2.400 eV, and if Bi in m-BiVO₄ is substituted by Sc (sub_Sc-Bi), the direct band gap will be reduced to 2.393 eV. However, if V is replaced by Sc (sub_Sc-V) as well as oxygen vacancy induced (sub_Sc–V+V_O), the band gap will become indirect with values of 1.913 and 2.198 eV, respectively. The reduction capability is in the sequence of sub_Sc–Bi > ideal > sub_Sc–V+V_O > sub_Sc–V, while the oxidation capability is in the order of ideal > sub_Sc–Bi > sub_Sc–V+V_O > sub_Sc–V . The «₁(0) of the ideal, sub_Sc–Bi, sub_Sc–V, and sub_Sc–V+V_O defective m-BiVO₄ are 8.290, 8.293, 12.791, and 8.285, respectively. The optical absorptions of ideal and sub_Sc–Bi m-BiVO₄ show anisotropy and they are nearly independent of the defect concentration. Sub_Sc–V m-BiVO₄ exhibits stronger absorption than the other three semiconductors. The absorptions of sub_Sc–V +V_O m-BiVO₄ vary widely with the defect concentrations, where 3.906% defect concentration of m-BiVO₄ has the strongest absorption. The estimated optical band gaps E^opt g are smaller than E_g for ideal and defective m-BiVO₄ .