Bonding, Fluctuations and Dynamics in Supercritical Metallic Fluids Using Synchrotron Radiation

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How are atoms condensed into metals and semiconductors? To understand this important question in solid state physics, we have studied static and dynamic structures for expanded fluid metals and semiconductors using synchrotron radiation at SPring-8. The present results are summarized as below.(1) Liquid and expanded fluid selenium (Se)Using high-resolution inelastic X-ray scattering technique, we found a peculiar narrowing of dynamic structure factor in liquid Se constituted of polymeric molecules. Expanded fluid Se undergoes the nonmetal-metal (NM-M) transition at high temperature and high pressure. We observed a clear increase of small angle scattering intensity in the transition region. At the same time excitation energy of the collective mode disperses twice as fast as the adiabatic sound velocity. These results hint that characteristic fluctuations are generated in the NM-M transition.(2) Short and medium range structures in liquid As_2Se_3Liquid As2Se3 undergoes the NM-M transition at high temperature and high pressure. We observed the increase of small angle scattering intensity but the profile was different from that in expanded fluid Se. Meanwhile no anomaly in the density dependence of the local structure was observed at the NM-M transition.(3) X-ray diffraction measurements of fluid sulfur (S)Nonmetallic liquid S is expanded into the vapor phase without the NM-M transition. We found that the well-separated first coordination shell is preserved in the supercritical region at high temperature and high pressure. Furthermore we observed the density region in which S dimeric molecules may be aggregate to form Si clusters.We plan to investigate the mechanism of the large speed-up of the dynamic sound velocity compared to the adiabatic one observed in the NM-M transition in order to understand deeply the characteristic fluctuations in the NM-M transition.