X-ray diffraction measurements for expanded fluid mercury up to the supercritical region

The energy-dispersive X-ray diffraction measurements for expanded fluid Hg have been carried out in the density region from 13.55 to 6.8 g cm⁻³ including the metal-non-metal transition region. It was found that the volume expansion of liquid Hg in the metallic region is not accompanied by a uniform increase of interatomic distance, r₁, but mainly caused by a decrease of coordination number, N₁. When the transition region is approached, the rate of decrease of N₁ becomes small and r₁ starts to elongate.