We show that the asymmetric crystal environment of the V site in the ladder compound NaV2O5 leads to a strong coupling of vanadium 3d electrons to phonons. This coupling causes fluctuations of the charge on the V ions, and favors a transition to a charge-ordered state at low temperatures. In the low temperature phase the charge fluctuations modulate the spin-spin superexchange interaction, resulting in a strong spin-phonon coupling.
@article{arxiv.cond-mat/9910403,
title = {Electron-phonon and spin-phonon coupling in NaV$_{2}$O$_{5}$: charge fluctuations effect},
author = {E. Ya. Sherman and M. Fischer and P. Lemmens and P. H. M. van Loosdrecht and G. Güntherodt},
journal= {arXiv preprint arXiv:cond-mat/9910403},
year = {2009}
}