Structure of liquid Rb-Se mixtures: void and fluctuation

Abstract

Neutron diffraction and EXAFS measurements, and the detailed structural modeling by reverse Monte Carlo 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 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 Sij(Q) for the RMC model indicates that the pre-peak is associated with the Se-Se interchain component of S(Q). From the void analysis using Delaunay simplices 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.