Observation of Structural Change with Possible Charge Disproportionation in Copper Vanadium Oxide Bronze β'-Cu0.65V2O5

We performed the X-ray diffraction measurements at low temperature under ambient pressure for the pressure-induced superconductor β'-Cu 0.65 V 2 O 5 . Satellite reflections were observed with an incommensurate modulation and a successive commensurate state depending on the cooling rate. The X-ray structure analysis in the commensurate state indicates the structural deformation on the vanadium ladder. We suggest the occurrence of the charge disproportionation for the origin of the structural transition. Additionally, we reveal the structural and electronic character for β (β')-vanadium bronzes.