STRUCTURAL MODIFICATIONS WITHIN COPPER(I) IODIDE AT PRESSURES UP TO 27 KBAR

Powder neutron diffraction measurements of copper(I) iodide at a tempe rature of 293 K and pressures up to 27 kbar are presented. A structura l phase transition is observed at a pressure of 16.3(1) kbar and invol ves a volume change of 4.1(1)%. Above the transition CuI is found to a dopt a rhombohedral structure, space group R3mBAR with Z = 2, alpha = 7.236(3) angstrom and alpha = 33.37(2)-degrees at p = 17.4(1) kbar. Th e I- ions essentially retain the cubic close-packed array adopted in t he ambient pressure zincblende phase, whilst the smaller Cu+ ions are rearranged over the available tetrahedral voids. No structural evidenc e has been found for the transitions around 4 and 5 kbar observed by o ther workers.