Asymmetrical bonding in liquid Bi disentangled by inelastic X-ray scattering

¹ Graduate School of integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8521, Japan
² Department of Physics, Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
³ Department of Physics, Keio University, Yokohama 223-8522, Japan
⁴ Japan Synchrotron Radiation Research Institute, SPring-8, Sayo-gun, Hyogo 679-5198, Japan
⁵ Materials Dynamics Laboratory, RIKEN SPring-8 Center, Sayo-gun, Hyogo 679-5148, Japan

^* e-mail: masinui@hiroshima-u.ac.jp

Published online: 21 August 2017

Abstract

The structure of liquid Bi has been debated in relationship with the Peierls distortion, as crystalline Bi takes A7 structure. A recent ab initio molec- ular dynamics simulation for liquid Bi predicted a flat-topped profile of the acoustic dispersion curve. To confirm the prediction, we have carried out inelas- tic x-ray scattering (IXS) for liquid Bi. The dynamic structure factor obtained by the IXS exhibits a distinct inelastic excitation of the longitudinal acoustic mode up to 14 nm⁻¹ and the dispersion curve of the excitation energy obtained by the memory function analysis becomes a flat-topped one. We found that a linear chain model including the interatomic interaction with the second near- est neighbors can explain the flat-topped profile. The result suggests that the anomalous dispersion curve in liquid Bi arises from local anisotropy related to the Peierls distortion in the crystalline phase. .