Lattice vibrations of alpha'-NaV2O5

TL;DR

This study investigates the lattice vibrations and phonon properties of alpha'-NaV2O5 using infrared, Raman, and lattice dynamics calculations, revealing the high-temperature phase symmetry and interpreting optical bands as phonon-assisted d-d transitions.

Contribution

It provides a comprehensive experimental and theoretical analysis of lattice vibrations and symmetry in alpha'-NaV2O5, including phonon assignment and interpretation of optical bands.

Findings

High-temperature phase has D_{2h}^{13} symmetry.

Infrared and Raman spectra are assigned to specific phonons.

Optical bands around 1 eV are phonon-assisted d-d transitions.

Abstract

We have measured far infrared reflectance and transmittance spectra as well as Raman scattering spectra of \alpha'-NaV2O5 single crystals for all the principal polarizations. The temperature range above the phase transition temperature T_c=35 K was investigated, mainly. On the basis of this experimental study and of the lattice dynamics calculations we conclude that the symmetry of NaV2O5 in the high temperature phase is described by the centrosymmetric D_{2h}^{13} space group. The assignment of the observed phonons is given. Values of dielectric constants are obtained from the infrared data. Asymmetric shapes of several infrared lines as well as higher order infrared vibrational spectra are discussed. The crystal field energy levels of the 3d electron localized at the V^{4+} site have been calculated in the framework of the exchange charge model using the values of effective charges obtained from the lattice dynamics calculations. According to the results of these calculations, the earlier observed broad optical bands in the region of 1 eV can be interpreted as phonon assisted d-d transitions.