Phase relations and structures of CuI phases at high prebures and temperatures

Using a multi-Anvil high-prebure device and synchrotron radiation, we have performed X-ray in situ observations of CuI under high prebure and high temperature up to 22 GPa and 1800 K in order to investigate the phase relations and crystal structures of high-prebure phases. The stability fields of CuI-IV, CuI-V, CuI-I , CuI-VII have been determined. A cubic rocksalt structured phase has been confirmed for the first time whereas CuI-VI was not observed. CuI-I shows continuous transition to the rocksalt phase, the mechanism of which is explained by the continuous increase in the amount of Cu ions that occupy the octahedral site. The newly observed rocksalt-Type phase is regarded as a disordered rocksalt phase since about 15 % of Cu ions are still in the tetrahedral site even at 20 GPa and 900 K. The CuI-I-To-CuI-VII phase boundary has a slight negative dT/dP slope below 6 GPa and a positive above 6 GPa.