XANES study of charge ordering on the spin-Peierls phase transition of alpha '-NaV2O5

alpha '- NaV2O5 transforms at T-C = 34K, and the origin of the phase transi tion seems to be caused by the charge order and spin-Peierls mechanism. How ever the experiments which reveal the existence of charge order are very li ttle. We measured XANES of V atoms which relates to the valence of V. It wa s found that the valences of V atoms in NaV2O5 were V4.5+ in the high tempe rature phase by comparing pre-edge and XANES of NaV2O5 with that of LiV2O5, CaV2O5 and V2O5. The analysis of EXAFS also shows the environment of the V 4.5+ state.