Incommensurate sulfur above 100 GPa

S-III, the high-pressure phase of sulfur stable above 80 GPa, is found to have the same incommensurately modulated monoclinic crystal structure as Te-III and Se-IV and is the first element observed to have a modulated structure above 100 GPa. A previously unreported phase is found between S-II and S-III on pressure decrease, and there is also evidence that the same phase exists on pressure increase. This phase has the same triclinic structure as Te-II and Se-III.