Substitutional alloy of Bi and Te at high pressure.

Being a best known thermoelectric material and a topological insulator at ambient condition, magic bismuth telluride (Bi2Te3) under pressure transforms into several superconducting phases, whose structures remain unsolved for decades. Here, we have solved the two long-puzzling low high-pressure phases as seven- and eightfold monoclinic structures, respectively, through particle-swarm optimization technique on crystal structure prediction. Above 14.4 GPa, we experimentally discovered that Bi2Te3 unexpectedly develops into a Bi-Te substitutional alloy by adopting a body-centered cubic disordered structure stable at least up to 52.1 GPa. The continuously monoclinic distortion leads to the ultimate formation of the Bi-Te alloy, which is attributed to the Bi→Te charge transfer under pressure. Our research provides a route to find alloys made of nonmetallic elements for a variety of applications.