HIGH-PRESSURE X-RAY-DIFFRACTION, ABSORPTION, LUMINESCENCE, AND RAMAN-SCATTERING STUDY OF CS2MOS4

Cesium thiomolybdate, Cs2MoS4, has been investigated at pressures up t o 12 GPa. Two phase transitions have been detected by absorption measu rements, Raman spectroscopy, and energy dispersive x-ray diffraction. The first phase transition to a monoclinic phase II [a=14.061(9) Angst rom, b=11.532(7) Angstrom, c=9.852(6) Angstrom, beta=97.14(6)degrees] has been observed at 8.0 GPa. The second transition at 9.7 GPa has bee n observed from the monoclinic phase II to an orthorhombic phase III [ a=12.085(4) Angstrom, b=15.707(6) Angstrom, c=11.828(5) Angstrom]. Abs orption and luminescence measurements have indicated an increase in th e absorption edge energy with pressure up to similar to 3 GPa. At pres sures greater than 3.5 GPa, the absorption energy decreases. Raman spe ctroscopy has revealed a low-frequency phonon mode with a negative pre ssure shift in the low-pressure phase I. The pressure-temperature phas e diagram has been determined up to 250 degrees C. The transition pres sures decrease linearly with slopes of similar to-0.013 GPa/degrees C. Models for the pressure-induced structural and electronic transitions are proposed.