Enhanced ionic conduction and disproportionation in pure CuCl at high pressure

Abstract The optical and electrical properties of pure cuprous chloride (CuCl) single crystals have been studied under pressure up to 12 GPa. The transition pressures for the three crystallographic phases have been determined as 5.1 ± 0.1 GPa (ZnS → tetragonal) and 8.8 ± 0.4 GPa (tetrag.-NaCl). During the transition at 5.1 GPa, where the coordination number changes, the formation of cupric ions is observed. This is interpreted as a result of a partial, transient, and reversible disproportionation. In the ZnS and NaCl phase, an enhanced ionic conductivity is found following the first transformation into the tetragonal structure. The concentration of the mobile ions is typically 10 18 cm −3 and their diffusivity is ∼ 4×10 −7 cm 2 s −1 . An applied voltage in excess of 0.7 V causes anodic oxidation of Cu + which mimics much higher conductivity.