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

Abstract

α′‐NaV2O5 transforms at TC = 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 V4.5+ 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 V4.5+ state.

Nanostructured Bilayered Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries

“…Oxidation state of material is essential for redox processes that are taking place in rechargeable batteries, and for that reason, we utilize X-ray absorption near-edge spectra (XANES) in the V K-edge range for the bilayered V 2 O 5 , orthorhombic V 2 O 5 (V 5þ standard), and VO 2 (V 4þ standard). The obtained values are consistent with the previous results of V 2 O 5 compounds 24,25 and show identical pre-edge shape and peak positions, implying that the V redox state in the bilayered V 2 O 5 sample is close to V 5þ , in a common VO 5 environment (Figure 4a). However, the area of the pre-edge peak for the bilayered is smaller than that of orthorhombic V 2 O 5 electrode.…”