Phase transitions of sulfur at high pressure: Influence of temperature and pressure environment

Abstract

Abstract Phase transitions of orthorhombic sulfur were investigated above 10 GPa by Raman spectroscopy using red light excitation. Transitions into several phases that have been reported in previous studies using green light excitation, are confirmed. The phase behaviour is observed to depend strongly on the preparation method. In the presence of a pressure transmitting medium (methanol/ethanol, 4:1), a sequence of phases α-S8 → [intermediate phase (“ip”) + S6] → [S6 + high pressure-low temperature phase (“hplt”)] is described and characterized. Without the use of a pressure transmitting medium, the phase sequence α-S8 → [“ip” + “hplt”] + “hplt” is observed. In addition, contributions of amorphous sulfur are detected around 10 GPa, i.e. at pressures below the transformation of α-S8 into the above-mentioned phases. Characteristic Raman spectra of the different phases are extracted and documented over a wide pressure range.