Structural Transition in Compressed Amorphous Sulfur

Properties of amorphous sulfur (a-S) were investigated by synchrotron x-ray diffraction up to 100 GPa between 40 and 175 K. Measurements of the structure factor yielded the radial distribution function and the densities of two amorphous forms. a-S undergoes a structural transition above 65 GPa, accompanied by density discontinuity of 7%. These results indicate the amorphous-amorphous transition, from a low-density to a high-density form, and open up the possibility for the direct measurements of density of liquid-amorphous materials at extreme conditions.