Structural Studies of Supercritical Fluid Metals using Synchrotron Radiation

我们对汞、Rb和Se等膨胀流体金属进行了结构研究，重点研究了金属-非金属(M-NM)转变。这些物质是M-NM跃迁离子随体积膨胀而发生的典型例子。HG是一种二价金属，发生威尔逊类型的M-NM转变。在流体Rb的M-NM转变中，电子关联被认为起着关键作用。Se是一种液体半导体，表现为半导体-金属-绝缘体的膨胀相变。我们利用Spring-8的同步辐射，测量了在温度高达2000K，气压高达2000bar的情况下，在液汽临界点周围从液体到稠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。我们已经积累了S(Q)、g(R)和S(q，ω)等静态和动态构造数据。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有很强的相关性。例如，流体汞的小角X射线散射测量表明，伴随着M-NM相变出现了一个微弱的密度涨落。从流体汞的非弹性X射线散射测量中，我们观察到在M-NM过渡区有一个快声音。声速是超音速的三倍。快声与时空尺度为nm和ps的局域结构的涨落有很强的联系，这可能导致M-NM相变。在Rb和Se方面，我们也取得了重要的结果。对于流体Rb，我们已经开发了一种钼电池，它的使用使我们能够研究直到超临界区域的结构。

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.