Raman Spectroscopic and X-Ray Diffraction Study of Sulfur under High Pressure

Raman spectrum and X-ray powder pattern of orthorhombic sulfur have been examined at pressures up to about 10 GPa. The Raman spectrum shows reversible phase transition at 5.2 GPa, while the X-ray diffraction pattern shows no sign of phase change up to 8.3 GPa. These contradictory results are explained as follows. A high-pressure phase exists above 5.2 GPa. In this pressure region, the metastable orthorhombic phase can also exist. The argon ion laser (λ=514.5 nm) used for Raman measurement induces a structural transformation from the orthorhombic phase to the high-pressure phase. The Raman spectrum suggests that the high-pressure phase is composed of chain molecules. In addition, evidence for interference between inter- and intramolecular bondings has been observed in this phase.