The influences of Nb and N dopants on elastic, electronic and optical properties of monoclinic BiVO4

Abstract

Monoclinic BiVO4 (m-BiVO4) is a novel semiconductor photocatalyst used for degradation of organic pollutants. Based on first principles study, the effects of Nb, N and Nb/N atoms on physical properties of 2 × 2 × 2 BiVO4 are investigated by considering their elastic properties, Debye temperature, electronic band structures, band edges and optical properties. Geometrical optimizations show that the lattice constants and angles of Nb-BiVO4, N-BiVO4, Nb/N-BiVO4 change slightly with respect to ideal BiVO4. Elastic properties indicate that Nb-BiVO4 is the stiffest and easily formed, Nb/N-BiVO4 is the most ductile, N-BiVO4 is the hardest. The values of Poisson’s ratio ν show the ionic bonding is dominated in ideal and defective BiVO4. Debye temperature θD of N-BiVO4 is the largest among all the materials considered. Ideal BiVO4 has direct band gaps of 2.095 eV while Nb-BiVO4, N-BiVO4 and Nb/N-BiVO4 have indirect band gaps of 2.014 eV, 1.871 eV and 1.823 eV, respectively. Band edge positions show that the reduction and oxidation capabilities are in the order of ideal BiVO4 > Nb-BiVO4 > N-BiVO4 > Nb/N-BiVO4, respectively. The static dielectric constants are 8.290, 8.382, 12.272 and 10.774 for ideal, Nb-BiVO4, N-BiVO4 and Nb/N-BiVO4, respectively. Compared with ideal BiVO4, red shifts occur in Nb-BiVO4, N-BiVO4 and Nb/N-BiVO4 which improve the visible-light absorption effectively. By Tauc’s relation, optical band gaps are estimated as 2.222 eV, 0.938 eV, 0.694 eV and 0.802 eV for ideal, Nb-BiVO4, N-BiVO4 and Nb/N-BiVO4, respectively. In addition, it is found that for ideal BiVO4, while for Nb-BiVO4, N-BiVO4 and Nb/N-BiVO4.