High pressure X-ray diffraction study of CdAl 2 Se 4 and raman study of AAl 2 Se 4 (A=Hg, Zn) and CdA l2 X 4 (X=Se, S)

We report the results of an X-ray diffraction study of CdAl 2 Se 4 and of Raman studies of HgAl 2 Se 4 and ZnAl 2 Se 4 at room temperature, and of CdAl 2 S 4 and CdAl 2 Se 4 at 80 K at high pressure. The ambient pressure phase of CdAl 2 Se 4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at 9 GPa is about 10%. The analysis of the Raman data of HgAl 2 Se 4 and ZnAl 2 Se 4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl 2 S 4 and CdAl 2 Se 4 , which shows a very weak temperature dependence of the Raman-active phonon modes.