X-ray diffraction measurements for expanded liquid mercury in the metallic region

X-ray diffraction measurements for expanded liquid Hg have been carried out for the first time in the density range from 13.55 to 10.26 g cm-3, covering almost all of the metallic region of expanded liquid Hg. The authors have developed a new type of high pressure vessel and a new sample cell made of single-crystal sapphire for the X-ray diffraction measurements using the energy-dispersive method. They have obtained the structure factor and the pair distribution function as functions of density. It was found that the nearest-neighbour distance remains almost constant increasing slightly, less than 1%, with the reduction of density by about 24%. On the contrary, the coordination number decreases substantially and almost linearly with decreasing density. The volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of interatomic distance but is mainly caused by a decrease of coordination number.