Superconductivity under high pressure in β(β′)-vanadium bronzes Original Research Article

The β(β′)-vanadium bronzes are quasi-one-dimensional conductors. Many of the members show metal–insulator transitions under ambient pressure, accompanying with the charge order. We have studied the pressure dependence of metal–insulator transition and the presence/absence of superconductivity under high pressure in β(β′)-vanadium bronzes. The superconductivity was observed in β-Na0.33V2O5 and β′-Cu0.65V2O5 but was absent in β-Sr0.33V2O5. In β-Na0.33V2O5 the metal–insulator transition is suppressed by pressure and a superconducting phase with appears around 8 GPa where the charge ordered phase collapses. On the other hand, a superconducting phase suddenly appears around 3 GPa and 6 K in β′-Cu0.65V2O5 which has no charge ordered phase.