Alternating sequence of ring and chain structures in sulphur at high pressure and temperature.

Sulphur is the subject of a renewed intensive research effort aiming at characterizing its complex phase diagram. Nonetheless, on reading recent literature on its high-pressure phases, a confused picture emerges where different techniques obtain different results. We have investigated the phase diagram of sulphur by X-ray diffraction at high pressures and temperatures (6-11 GPa and 300-1,000 K), and have observed a new occurrence of a molecular S6 phase, in addition to the previously described polymeric helical trigonal and tetragonal phases.