Phase Diagram of the System Copper(I) Iodide + Cesium Iodide

The phase equilibrium diagram for the CuI + CsI system has been redetermined by differential scanning calorimetry and X-ray diffraction. The phase diagram exhibits three intermediate compoundsCs3Cu2I5, melting incongruently at 663.0 K, CsCu2I3, melting congruently at 656.0 K, and CsCu9I10, undergoing a solid-state disproportionation reaction to CuI + CsCu2I3 at 604.8 K. The existence of CsCu9I10, derived from DSC studies in accordance with the phase rule, is not shown by X-ray diffraction investigations.