High-pressure structural study of CuAlS2 and CuAlSe2

The chalcopyrite compounds CuAlS2 and CuAlSe2 have been studied by energy d ispersive X-ray diffraction up to 25 GPa. On the upstroke, pressure-induced first-order phase transitions from the chalcopyrite structure to a cubic s tructure, probably of the rock-salt type, were observed at 14.3 and 12.4 GP a, respectively. It has been impossible to index the diffraction pattern ob tained at ambient conditions after a pressure cycle for CuAlS2. For CuAlSe2 only a broadening of the diffraction peaks has been observed after the pre ssure cycle. The experimental data have shown a decrease under pressure of the structural parameter epsilon = 2 - c/a. A first-order Murnaghan equatio n of state used to fit the experimental PV data in the chalcopyrite phase g ives the values of the bulk moduli: (99 +/- 3) GPa for CuAls(2) and (85 +/- 2) GPa for CuAlSe2, both with a fixed B' = 4.