Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb₃Rh₇O₁₅

The mixed-valent Pb₃Rh₇O₁₅ undergoes a Verwey-type transition at T_v ≈ 180 K, below which the development of Rh³⁺/Rh⁴⁺ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb₃Rh₇O₁₅ by measuring its electrical resistivity under hydrostatic pressures up to 8 GPa with a cubic anvil cell apparatus. We fnd that the application of high pressure can suppress the Verwey-type transition around 3 GPa, above which a metallic state is realized at temperatures below ∼70 K, suggesting the melting of charge order by pressure. Interestingly, the lowerature metallic region shrinks gradually upon further increasing pressure and disappears completely at > 7 GPa, which indicates that the charge carriers in Pb3Rh₇O₁₅ undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb3Rh7O₁₅ and compared to that of Fe₃O₄, showing an archetype Verwey transition.