用SPring-8同步辐射研究流体水银的结构变化和金属-非金属转变

随着从液态到气态的连续体积膨胀，在临界点附近，典型的液态金属水银经历了金属-非金属（M-NM）。在Spring-8的BL04B1高温高压实验站，利用同步辐射白光，采用能量色散X射线衍射（EDXD）方法，我们研究了流体水银从液体到稠密气态的宽广密度范围中的结构变化。实验方面，我们成功地开发出一个新的高压容器，它具有7个出射窗口用于收集散射X射线，测量的温度和压力上限分别是1700℃和2000bar，适合于在高温和高压下对流体物质进行能量色散X射线衍射测量。结果表明，流体水银的结构因子S(k)的精确性和可靠性有了很大的提高，并获得了流体水银的配位数和配位距离与密度变化之间的准确关系。我们发现，除了存在由配位数减少所导致的非均匀膨胀阶段之外，在水银的金属-非金属转变时还存在一新的均匀膨胀现象，即配位距离随密度减少呈线性增长阶段。基于这些新的结果，我们提出了流体水银的膨胀模型，并讨论了流体水银的金属-非金属转变与结构的关系。

Structural studies of fluid mercury using synchrotron radiation at SPring-8

With the volume expansion by heating up toward the critical point, typical liquid metal mercury undergoes metal-nonmetal transition (M-NM) at a density around 9 g/cm3. To study the structure changes of fluid Hg during volume expansion, we have carried out X-ray diffraction measurements for expanded fluid mercury in a wide density region from liquid to dense vapour region using synchrotron radiation at SPring-8. We have succeeded in developing a new high-pressure vessel, up to 1700C under 2000 bar and with 7 scattering windows for energy-dispersive X-ray diffraction (EDXD) measurements under high temperature and high pressure. It was found that the reliability of the structure factors, S(k), and the accuracy of the pair distribution functions, g(r), are much better. Reliable relations of the coordination number and the correlation distance with the density of fluid Hg were obtained. Structural model of volume expansion of fluid Hg is proposed based on our new results. Structural changes with decreasing density are discussed in relation to the M-NM transition in fluid Hg.