A computational study of the thortveitite structure of zinc pyrovanadate, Zn₂V₂O₇, under pressure

We performed a pressure-driven study of zinc pyrovanadate, Zn₂V₂O₇, using the first-principles approach under the framework of density functional theory (DFT). Zn₂V₂O₇ crystalizes in a monoclinic (α-phase) structure with the space group C2/c at ambient pressure. In comparison with the ambient phase, there are four different high-pressure phases, namely β, γ, κ and δ, found at 0.7, 3.8, 4.8 and 5.3 GPa, respectively. The detailed crystallographic analysis as well as their structures is consistent with the theory and experiment reported in the literature. All phases including the ambient phase are mechanically stable, elastically anisotropic and malleable. The compressibility of the studied pyrovanadate is higher than that of the other meta- and pyrovanadates. The energy dispersion of these studied phases reveals that they are indirect band gap semiconductors with wide band gap energies. The band gap energies follow a reduced trend with pressure except the κ-phase. The effective masses for all of these studied phases were computed from their corresponding band structures. The values of energy gaps obtained from the band structures are almost similar to the optical band gap obtained from the optical absorption spectra, as estimated by the Wood-Tauc theory.