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Electronic Topological Transition in Ag2Te at High-pressure
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Recently, Ag2Te was experimentally confirmed to be a 3D topological insulator (TI) at ambient pressure; however, the high-pressure behaviors and properties of Ag2Te were rarely and ambiguously reported.  A team from state key lab of Superhard materials in Jilin university has gained insight into the mysterious structure and function of Ag2Te. Their research has been published on September 30th, 2015 in Scientific Reports.

Based on the in-situ high pressure synchrotron X-ray diffraction at the 4W2 High-Pressure Station of Beijing Synchrotron Radiation Facility (BSRF), the team identified really interesting the high-pressure behaviors of Ag2Te. They show that Ag2Te undergoes twice structural phase transition around 2.2 GPa and 11.3 GPa. The accurate pressure-induced phase transition sequence is firstly determined as P21/c, Cmca, Pnma. It is worth noting that the reported isostructural P21/c phase is not existed, and the reported structure of Cmca phase is corrected by CALYPSO methodology. The second high-pressure structure, a long puzzle to previous reports, is assigned to Pnma phase by this team.

Meanwhile, they present a pressure-induced electronic topological transition is firstly found in Ag2Te at 1.8 GPa. Before the electronic topological transition (ETT), there is a positive pressure coefficient of bulk band-gap, which is firstly found in the topological insulators family. After the ETT, the band gap of Ag2Te, indirect band-gap semiconductor, is changed into direct band-gap.

Thus, for Ag2Te, it is verified that pressure is helpful for increasing the topological nature by inducing the increase of the bulk band-gap. Their results provide an approach of enhancing the topological nature of topological insulators by physical and chemical methods.

The phase transformation process of Ag2Te


Yuhang Zhang, Yan Li*, Yanmei Ma, Yuwei Li, Guanghui Li, Xuecheng Shao, Hui Wang, Tian Cui, Xin Wang* & Pinwen Zhu* Electronic Topological Transition in Ag2Te at High-pressure. Scientific Reports 5(2010), 14681(1–9).

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