High-Pressure Phase Transitions and Structures of Topological Insulator BiTeI

Abstract

Being a giant bulk Rashba semiconductor, the ambient-pressure phase of BiTeI was predicted to transform into a topological insulator under pressure at 1.7–4.1 GPa [Nat. Commun. 2012, 3, 679]. Because the structure governs the new quantum state of matter, it is essential to establish the high-pressure phase transitions and structures of BiTeI for better understanding its topological nature. Here, we report a joint theoretical and experimental study up to 30 GPa to uncover two orthorhombic high-pressure phases of <i>Pnma</i> and <i>P</i>4/<i>nmm</i> structures named phases II and III, respectively. Phases II (stable at 8.8–18.9 GPa) and III (stable at >18.9 GPa) were first predicted by our first-principles structure prediction calculations based on the calypso method and subsequently confirmed by our high-pressure powder X-ray diffraction experiment. Phase II can be regarded as a partially ionic structure, consisting of positively charged (BiTe)⁺ ladders and negatively charged I^– ions. Phase III is a typical ionic structure characterized by interconnected cubic building blocks of Te–Bi–I stacking. Application of pressures up to 30 GPa tuned effectively the electronic properties of BiTeI from a topological insulator to a normal semiconductor and eventually a metal having a potential of superconductivity