Short- and Intermediate-Range Structures of Liquid Rb-Se Mixtures(Condensed Matter : Structure, Mechanical and Thermal Properties)

Extended X-ray absorption fine structure (EXAFS) and neutron diffraction measurements, and the detailed structural modeling by reverse Monte Carlo (RMC) simulation have been performed in order to study the short- and intermediate-range structures of liquid Rb-Se mixtures. The Se chains in the liquid mixture are strongly bent to form horseshoe-like Se chains with Rb atoms at the chain ends, creating a large amount of voids. The interaction between Rb and Se atoms is very weak and Rb atoms come close together. Near the boundary of the miscibility gap at low temperature the short Se chains link up to form a large cluster, and Rb atoms sit around it. The structure factor S(Q) in the liquid mixture has a small pre-peak at 〜1.3Å^<-1>. The computed partial S_<ij>(Q) for the RMC model indicates that the pre-peak is associated with the Se-Se interchain component of S(Q). The voids in the structure play an important role in the appearance of the pre-peak in S(Q). From the void analysis using Delaunay tessellation it has been revealed that the observed pre-peak corresponds to a pre-peak in the concentration-concentration structure factor due to the chemically ordered packing of the voids and Se chains in the structure.