Complex crystal structures of Te-II and Se-III at high pressure

Te-II, the high-pressure phase of tellurium stable between 4 and 7 GPa, is found to have a triclinic structure that is previously unknown in the elements, but which is closely related to the incommensurate Te-III structure. Se-III is found to be isostructural with Te-II. The appearance of additional weak reflections in Te-II profiles below 4.3(1) GPa suggests the existence of a previously unknown phase which might be related to Se-II.