Charge disproportionation in quasi-one-dimensional vanadium oxides

The vanadium bronzes β ( β ′ )- AxV 2O5 (A=Na+, Ag+, Ca2+, Cu+) are investigated by electron energy-loss spectroscopy (EELS), X-ray absorption near edge spectroscopy and electronic structure calculations. We analysed the fine structural features of experimental spectra in the low-loss region and the vanadium L2,3 and oxygen K ionization edges in correlation with electronic structure of this quasi-one-dimensional conducting system. The different energy separations on the fine structures of the vanadium L3 edge and oxygen K edge arising from ligand field splitting suggest charge disproportionation occurring in β ( β ′ )- AxV 2O5 materials at room temperature. Based on the analysis of the highly-damped valence electron plasmon peak for these materials, the charge distribution among different chains and ladders is briefly discussed.