Structural Studies of Supercritical Fluid Metals using Synchrotron Radiation

我们对膨胀流体金属如Hg、Rb和Se进行了结构研究，重点研究了金属-非金属（M-NM）转变。这些物质是M-NM迁移离子随体积膨胀而发生的典型例子。汞是一种二价金属，发生威尔森型的M-NM跃迁。在流体Rb的M-NM跃迁中，电子相关被认为起着关键作用。硒是一种液体半导体，随着膨胀表现出半导体-金属-绝缘体的转变。我们利用同步辐射在SPring-8测量了温度高达2000k，压力高达2000bar的He气体压缩下，在液-气临界点附近从液体到致密蒸汽的宽密度区域内的x射线衍射、小角x射线散射和非弹性x射线散射。我们积累了S(Q)、g(r)、S（Q,ω）等静态和动态结构数据。我们已经获得了重要的结果，表明M-NM转变与结构变化之间存在很强的相关性。例如，流体Hg的小角度x射线散射测量表明，伴随M-NM转变出现了微弱的密度波动。从流体汞的非弹性x射线散射测量中，我们观察到在M-NM过渡区有一个快速的声音。声速是超声波速度的三倍。快速声与局部结构的波动密切相关，其时空尺度为nm和ps，可能诱发M-NM跃迁。在Rb和Se中我们也得到了重要的结果。对于流体Rb，我们开发了一种钼电池，它的使用使我们能够进行超临界区域的结构研究。

We have performed structural investigations on expanded fluid metals such as Hg, Rb and Se focusing on the metal-nonmetal (M-NM) transition. These substances are typical examples in which the M-NM transit ion occurs with volume expansion. Hg is a divalent metal and the M-NM transition with the Wilson type takes place. In the M-NM transition of fluid Rb the electron correlation is considered to play a key role. Se is a liquid semiconductor which shows the semiconductor-metal-insulator transition with expansion.We have measured x-ray diffraction, small angle x-ray scattering and inelastic x-ray scattering at temperatures up to 2000 K and pressures up to 2000 bar with He gas compression, in the wide density region from liquid to dense vapor surrounding the liquid-vapor critical point, by the use of synchrotron radiation at SPring-8. We have accumulated structural data of static and dynamic ones such as S(Q), g(r) and S(Q,ω). We have obtained important results showing strong correlation between the M-NM transition and the structural change. For example, small angle x-ray scattering measurements for fluid Hg reveals that a weak density fluctuation appears accompanying the M-NM transition. From the inelastic x-ray scattering measurement for fluid Hg we have observed a fast sound at the M-NM transition region. The sound velocity is triple the ultrasonic velocity. The fast sound is strongly connected with the fluctuation in the local structure with the time-and-space scale of nm and ps which may induce the M-NM transition. In Rb and Se we have also obtained important results. For fluid Rb we have developed a molybdenum cell the use of which enabled us the structural studies up to the supercritical region.