Bi-centric view of the isostructural phase transitions in α-Bi2 Se3 and α-Bi2 Te3 (Phys. Status Solidi B 7/2017)

Most of the A2B3-type three-dimensional (3D) topological insulators (TIs) have been reported to exhibit a pressureinduced isostructural phase transition (IPT) in the low-pressure region; however, the underlying mechanism remained elusive in past years. Here (article no. 1700007), Hailiang Zhu et al. comparatively investigated the IPTs in archetypical TIs of α-Bi2Se3 and α-Bi2Te3 from Bi-centric view by using high-pressure X-ray absorption spectroscopy. Near IPT, a sudden decrease is observed for Bi L3-edge absorption energy. More surprisingly, Bi–Se2 (Te2) and Bi–Se1 (Te1) bond distances simultaneously exhibit abnormal elongations and abrupt increases for their Debye– Waller factors, in contrast to the monotonous compression of Bi–Bi bond distance. Theoretical calculations also reveal an extremely small energy barrier for the structural distortion associated with IPT. These results indicate that the quintuple layer units of Se2 (Te2)–Bi–Se1 (Te1)–Bi–Se2 (Te2) shrink parallel to the layers but elongate perpendicular to the layers during IPT, which is associated with enhanced structural disorder. Therefore, the authors' findings suggest that the IPTs in most A2B3-type 3D TIs would be coupled with charge redistribution and structural distortion accompanied with static structural disorder increase.