Unraveling the Structure-Raman Spectra Relationships in V2O5 Polymorphs via a Comprehensive Experimental and DFT Study

Vanadium pentoxide polymorphs (alpha-, beta-, gamma'-, and epsilon'-V2O5) have been studied using the Raman spectroscopy and quantum-chemical calculations based on density functional theory. All crystal structures have been optimized by minimizing the total energy with respect to the lattice parameters and the positions of atoms in the unit cell. The structural optimization has been followed by the analysis of the phonon states in the Gamma-point of the Brillouin zone, and the analysis has been completed by the computation of the Raman scattering intensities of the vibrational modes of the structures. The optimized structural characteristics compare well with the experimental data, and the calculated Raman spectra match the experimental ones remarkably well. With the good agreement between the spectra, a reliable assignment of the observed Raman peaks to the vibrations of specific structurals units in the V2O5 lattices is proposed. The obtained results support the viewpoint on the layered structure of vanadium pentoxide polymorphs as an ensemble of V2O5 chains held together by weaker interchain and interlayer interactions. Similarities and distinctions in the Raman spectra of the polymorphs have been highlighted, and the analysis of the experimental and computational data allows us, for the first time, to put forward spectrum-structure correlations for the four V2O5 structures. These findings are of the utmost importance for an efficient use of Raman spectroscopy to probe the changes at the atomic scale in the V2O5-based materials under electrochemical operation.