Void structure and intermediate-range fluctuations in the metal-nonmetal transition range in expanded liquid Hg

The reverse Monte Carlo and Voronoi-Delaunay analyses have been applied to characterize the intermediate-range fluctuations near the metal-nonmetal transition in expanded liquid Hg. An analysis of voids acts as a useful adjunct to the normally discussed structural properties in interpreting the origin of intermediate-range fluctuations in the expanded liquids. The results for Hg-based and void-based partial pair distribution functions and the partial coordination number distributions reveal that the metallic domains (M domains) are built with packing of tetrahedral Hg(4) blocks. The M domains transform into the nonmetallic domains (NM domains) creating large voids (L voids) similar to 3.1 A degrees in radius, which are supported by the network linked with tetrahedral Hg(4) blocks containing small voids (S voids) similar to 2.3 A degrees in radius at densities of 9.2-10.5 g cm(-3), where the coordination number is rapidly reduced below six. The estimated density variations in S(cc)(')(0) from "domain model" and "void model" exhibit a peak around 10.5 g cm(-3), which indicates that M domains and NM domains coexist near the metal-nonmetal transition region. There appears the prepeak at 0.8-1.2 A degrees(-1) in the partial structure factor of L voids around the L voids, S(LV-LV)(')(Q), suggesting the chemical ordering of L voids. It follows that the intermediate-range concentration fluctuations resulting in microphase separation (clustering) of NM domains and M domains are reflected in the structural change near the metal-nonmetal transition.