Optical Absorption and X-Ray Diffraction Studies of Sulfur Under High Pressure

In situ high pressure optical absorption measurements of sulfur have been carried out by using DAC device with a TASCO V-550 UV-VIS spectrophotometer at pressures up to 41.6GPa. The curves of absorption edge vs pressure were obtained, in which there are two turning points at about 5 and 12GPa, corresponding to two changes of colour in the optical observation: one is from yellow to red and the other from red to black at 5-6.5 and 10-12GPa, respectively. The absorption edge reaches above 800nm when the pressure is increased to 23GPa. The structure and phase transitions have also been investigated by using in situ high pressure energy-dispersive x-ray diffraction with synchrotron radiation at pressures up to 33.7GPa. No structure phase transition occurs at 5-6 GPa, but there is a new high-pressure phase, caused probably by the reorientation or ordering of S₈.