Voids and Intermediate-Range Order in Network-Forming Liquids

• Published in: Journal of the Physical Society of Japan 2007-07, Vol.76 (7)
• Main Authors: Maruyama, Kenji, Endo, Hirohisa, Hoshino, Hideoki
• Format: Article
• Language: English
• ISSN: 0031-9015; 1347-4073

The RMC and Voronoi-Delaunay analyses were applied to study the void structure in the network-forming liquids: Rb20Se80 and BiBr3. The distribution function of the relative positions of atoms and void centers in space, the coordination number of atoms and voids around a void and the size distribution of voids were examined using the previous experimental data for S(Q) to characterize the connectivity of the bonding network supporting voids and the intermediate-range correlation as manifested in the pre-peak of S(Q). The voids in l-Rb20Se80 are formed by the 8-membered ring-like Se chains. A Rb cluster composed of 3-4 Rb atoms replaces one of five void sites and binds ∼4 Se rings involving voids around it through the interactions between Rb and Se and between Rb and Rb. In l-BiBr3 the hexagonal cages involving voids are formed by the corner-sharing of the trigonal pyramidal BiBr3 blocks. The strong preference of Bi ion for three-fold coordination helps to bind between the neighboring cages and to construct a honeycomb network in highly correlated fashion. The pre-peak of the observed S(Q) indicative of the intermediate-range order arises from the correlation between the neighboring Se rings in l-Rb20Se80 and between the neighboring hexagonal cages formed by BiBr3 blocks in l-BiBr3. In conclusion the pre-peak of S(Q) in l-Rb20Se80 and l-BiBr3 is related to the pre-peak of the void-based concentration-concentration structure factor S'CC(Q) due to an intermediate chemical order in the structure.