Pressure-induced structural transitions, alloying and superconductivity in topological insulators Bi2Te2Se and Bi2Se2Te†
Abstract
Over the past decade, external pressure has been found to play an important role in modulating the structures and properties of sesqui-chalcogenides, but several key puzzles still remain to be solved. In this work, pressure-induced structural phase transitions, alloying and topological superconductivity in the ternary tetradymites Bi2Te2Se and Bi2Se2Te were investigated via in situ high-pressure angle-dispersive X-ray diffraction and resistance measurements. Both of them transform from the layered rhombohedral Rm structure to a 7-fold monoclinic C2/m phase, then to an 8-fold monoclinic C2/c structure, and eventually to a bcc alloy, which are quite different from previous work, but similar to the transitions in Bi2Te3. The superconductivity was found in the rhombohedral structure of Bi2Se2Te with Tc ≈ 2.2 K at 4.3 GPa, which should be related to the topological quantum transition. Furthermore, the atomic size and element electronegativity were discovered to have a significant effect on the alloying and amorphization of these compounds.