"Tuning the crystal structure and electronic states of Ag2Se : Structural transitions and metallization under pressure"

Zhao Zhao: Shibing Wang, Artem R. Oganov, Pengcheng Chen, Zhenxian Liu, and Wendy L. Mao; Phys. Rev B89, 05/22/14.

Additional Authors: Shibing Wang, Artem R. Oganov, Pengcheng Chen, Zhenxian Liu, and Wendy L. Mao

Abstract:

We performed synchrotron x-ray diffraction and infrared (IR) experiments combined with evolutionary structure predictions and band structure calculations on Ag2  Se to ∼20 GPa. We present evidence for phase I (β-Ag2 Se ) as a potential three-dimensional topological insulator by its increase in optical band gap and the topologically nontrivial nature of its band structure. Higher pressures induce a triple-layer stacking pattern and significantly increase the crystallographic inequivalence of the two Ag sites, where P21 21 21   phase I first reconstructs into a Pnma phase II, and then transforms into a topologically different Cmcm phase III. The radical changes in IR spectra and electronic band structures indicate the metallic nature of the high-pressure phases. Our results highlight the effects of pressure in tuning the crystal structure and electronic states of Ag2Se .