XANES study of charge ordering on the spin-Peierls phase transition of α′-NaV₂O₅

α′-NaV₂O₅ transforms at T_C = 34 K, and the origin of the phase transition seems to be caused by the charge order and spin-Peierls mechanism. However the experiments which reveal the existence of charge order are very little. We measured XANES of V atoms which relates to the valence of V. It was found that the valences of V atoms in NaV₂O₅ were V^4.5+ in the high temperature phase by comparing pre-edge and XANES of NaV₂O₅ with that of LiV$_₂O₅, CaV₂O₅ and V₂O₅. The analysis of EXAFS also shows the environment of the V^4.5+ state.