Structural Studies of Supercritical Fluid Metals using Synchrotron Radiation

我们已经进行了结构研究的扩展流体金属，如汞，Rb和硒的金属-非金属（M-NM）过渡的重点。这些物质是典型的例子，其中M-NM过渡离子发生体积膨胀。Hg是二价金属，发生Wilson型的M-NM跃迁。在流体Rb的M-NM跃迁中，电子关联起着关键的作用。Se是一种液态半导体，它表现出膨胀的超导体-金属-绝缘体转变，我们测量了在2000 K和2000 bar压力下，在从液态到稠密蒸气的宽密度区，在液-汽临界点附近的He气体压缩下的X射线衍射、小角X射线散射和非弹性X射线散射，利用SPring-8上的同步辐射积累了S（Q），g（r），S（Q，ω）等静态和动态的结构数据。我们得到了重要的结果，表明M-NM跃迁和结构变化之间的强相关性。例如，流体Hg的小角X射线散射测量显示，伴随着M-NM转变出现了弱的密度波动。从流体Hg的非弹性X射线散射测量中，我们观察到在M-NM过渡区的快声。声速是超声波速度的三倍。快声与局域结构中nm和ps时空尺度的涨落密切相关，这种涨落可能导致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，我们已经开发了一个钼电池，使用它使我们的结构研究到超临界区域。

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.