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

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..