The electronic structure of α-V2O5, γ′-V2O5, and γ-MeV2O5 (Me = Li, Na) bronzes is studied by quantum-chemical calculations completed by spectroscopic experiments. The calculations are performed using the G0W0 method with the DFT+U self-consistent wave function as an initial approximation. The electronic band gap Eg = 2.89 eV calculated for α-V2O5 is found to be in fair agreement with available experimental data. The strategy was then applied to studying the electronic structure of the γ′-V2O5 phase and γ-MeV2O5 bronzes for which no experimental band gap data exist in the literature. Computed Eg values are equal to 3.17, 1.21 and 1.18 eV for γ′-V2O5, γ-LiV2O5, and γ-NaV2O5, respectively. The nature of the alkali metal atom is determined to have little influence on the structure and electronic states of the bronzes. Raman spectra recorded with different wavelengths of exciting radiation have allowed the determination of the energy threshold corresponding to the transition from off-resonance to resonance Raman scattering process. In this way, a band gap value in the range 2.54-2.71 eV for α-V2O5 and γ′-V2O5 is obtained in good agreement with the experimental values for the α-phase. Raman spectra of γ-MeV2O5 suggest the band gap smaller than 1.58 eV in these materials, whereas the photoluminescence measurements yield Eg ≈ 0.95 eV for the γ-LiV2O5 bronze. Remarkably, the result of the G0W0 calculations lies in between the experimental estimates. The strong similarity of structures and electronic states of γ-LiV2O5 and γ-NaV2O5 accounts for their the same operating voltage when used as cathodes in Li(Na)-ion batteries.
Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films