X-ray diffraction studies of expanded fluid mercury using synchrotron radiation

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Abstract
Energy-dispersive x-ray diffraction measurements using synchrotron radiation at SPring-8 for expanded fluid Hg were carried out over the wide density range from the liquid to the dense-vapour region including the metal-non-metal (M-NM) transition region. The density ranges from 13.6 to . We developed a high-pressure vessel and a sapphire cell for the x-ray diffraction measurements under high temperature and pressure up to and 1765 bar. We obtained the structure factor S(k) and the pair distribution functions g(r). The density variations of the interatomic distance and coordination number obtained were discussed in relation to the M-NM transition in fluid Hg. It was found that the volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of , but is mainly caused by a decrease of . When the transition region is crossed, the rate of decrease of becomes small and starts to elongate. We discussed some previous band calculations for expanded fluid Hg and concluded that it is essential for explaining the M-NM transition in liquid Hg to take the fluctuation of into account. When the density decreases down to the dense-vapour region, the first maxima of g(r) are located at around 3.3-3.4 Å, which is close to the interatomic distance of Hg dimers.