BAND-STRUCTURE AND STRUCTURAL STABILITY OF THE HIGH-PRESSURE PHASES OF THE GROUP VIB ELEMENTS

The group VIb elements, such as sulfur, selenium and tellurium, exhibi t similar successive structural phase transitions under pressure. The electronic band-structure of the high-pressure phases of these element s is investigated on the basis of first principles calculation. In par ticular, the structural stability of the beta-Po type rhombohedral pha se of selenium has been studied, and the result suggests that the rhom bohedral structure becomes unstable owing to monoclinic distortion.