Niobium Doping in BiVO4 : Interplay Between Effective Mass, Stability, and Pressure

Abstract

We have applied density functional theory to study the electronic structure changes caused by Nb incorporation in BiVO₄ and the application of external pressure. The overall solubility of Nb in BiVO₄ is usually high, and the presence of oxygen vacancies affect the dopability of Nb in BiVO₄ . Through the analyses of the chemical-potential landscape, we have determined the single-phase stability zone of BiVO₄ with the Nb doping. The most favorable Nb doping is simultaneous substitutions at both V- and Bi-sites. Even though Nb substitution at only V-site is next favorable, the band gap change is not very significant which agrees with an earlier experiment. However, it does change the electron effective mass by 20 % owing to the presence of Nb 4d bands in the conduction bands, which explains better catalytic activity by Nb-doped BiVO₄ . In addition, application of external pressure the single-phase stability zone in the chemical-potential landscape. We have also focused on the local structural distortions near the Nb doping site, especially on the BiO₈ octahedra. We have shown here that pressure-induced symmetrization of BiO₈ dodecahedron lowers the electron's effective mass further and therefore can help to improve the photoconduction property of BiVO₄ .

Keywords: Band theory; density functional theory (DFT); hydrogen production; photocatalysis; polaron conduction.