The structural properties were investigated at high pressures and temperatures by using neutron powder diffraction techniques to monitor the effects of pressure upon the superionic properties. Upon increasing the temperature, at a pressure of 1.31GPa, 3 structural phase transitions were observed. The first was from the room-temperature zincblende phase, to rhombohedral CuI at 444K. There was only limited cation disorder in the latter, and this increased gradually with temperature. The preferred locations of interstitial cations were sites between tetrahedral and octahedral interstices within the slightly distorted face-centered cubic anion sub-lattice. A subsequent transition to a disordered face-centered cubic phase occurred at 694K. This phase exhibited complete cation disorder at all measured pressures and temperatures. Finally, the iodide underwent a further phase transition at 920K. Initial studies indicated that this phase was a body-centered cubic superionic, with complete disorder of the cation sub-lattice. The cations were found to occupy tetrahedral sites preferentially, as in α-AgI and α-CuBr.

S.Hull, D.A.Keen, W.Hayes, N.J.G.Gardner: Journal of Physics - Condensed Matter, 1998, 10[48], 10941-54