Local structural changes during the disordered substitutional alloy transition in Bi2Te3 by high-pressure XAFS

• Published in: Journal of applied physics 2018-08, Vol.124 (6)
• Main Authors: Guo, Zhiying, Zhu, Hailiang, Dong, Juncai, Jia, Quanjie, Gong, Yu, Wang, Yan, Li, Haijing, An, Pengfei, Yang, Dongliang, Zhao, Yidong, Xing, Haiying, Li, Xiaodong, Chen, Dongliang
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5042457

A2B3-type 3D topological insulators, Bi2Te3 and Sb2Te3, have been reported to transform into disordered substitutional alloys under high pressure. However, γ → δ phase transition and the local structure changes around Bi during the formation of the disordered Bi-Te binary alloy in Bi2Te3 still remain unclear. Here, high-pressure X-ray absorption fine structure (XAFS) combined with high-pressure X-ray diffraction has been used to explore the local structural transformations in the three structural phase transitions of Bi2Te3. The Bi L3-X-ray absorbing near edge structure (XANES) spectra of δ-Bi2Te3 clearly showed that a new absorption feature at energy of about 13 465 eV would emerge during the γ → δ phase transition. Through simulation of the XANES spectra by varying the cluster size, we confirmed that the new absorption peak arises from the medium-range order in bcc structure. The Bi L3-EXAFS results in δ phase reveal that the Bi atoms in the third shell exhibit abnormal elongations with pressure until merging with the shrinking Te shell. Our findings indicate a two-step structural transition of the disordered substitutional alloys via an ordered bcc intermediate phase.