Polarized Raman spectra of the calcium vanadium oxide bronze beta-Ca0.33V2O5 are measured in the temperature range between 300 K and 20 K. The charge ordering phase transition at about 150 K is characterized by the appearance of the new Raman-active modes in the spectra, and by anomalies in the electronic background scattering. The high temperature Raman scattering spectra of beta-Ca0.33V2O5 are in apparent resemblance with those of alpha'-NaV2O5, which suggests that there is a similar charge-phonon dynamics in both compounds. The study of dynamical properties and the symmetry analysis of the Raman modes show that in the mixed valence state of beta-Ca0.33V2O5 the electrons are delocalized into V1-O5-V3 orbitals. We propose that in the charge ordered state below 150 K the d-electrons localize within V1-V3 ladders, either in "zig-zag" fashion like in alpha'-NaV2O5 or in the forms of the double chains like in gamma-LiV2O5.
@article{arxiv.cond-mat/0301477,
title = {Raman scattering study of charge ordering in beta-Ca0.33V2O5},
author = {Z. V. Popovic and M. J. Konstantinovic and V. V. Moshchalkov and M. Isobe and Y. Ueda},
journal= {arXiv preprint arXiv:cond-mat/0301477},
year = {2009}
}
Comments
5 pages, 4 figs incl. in the text. J.Phys.:Condens.Mater 15, (2003) in press