Structural properties of liquid alkali-metal–lead alloys: NaPb, KPb, RbPb, and CsPb

Abstract

The structural properties of liquid equiatomic alkali-metallead alloys APb, with A =Na, K, Rb, and Cs, have been studied with neutron diffraction. The experimental data are reduced to the neutron-weighted total structure factors S(Q) and radial distribution functions n (r). In all the systetns studied, S(Q) is characterized by a first sharp diffraction peak (FSDP) at Q -I A ' and n (r) 0 by structure in the first coordination shell at r = 3 -4 A, both features indicating the presence of polyatomic structural units. Two types of structural models have been fitted to the experimental data, both based on consideration of such units: the random packing of structural units model, and the reference interaction site model. The structures of the units are derived from powder-diffraction measurements made with the same instrument on solid polycrystalline samples. Allowing for a slight expansion of the units on melting and using physically reasonable values for the adjustable parameters, both models give satisfactory agreement with the experimental data and are used to give the partial structure factors and pair distribution functions. Inelastic-scattering measurements have been made on one system, liquid KPb, using a spectrometer at the same source. These yield a value for the mean difFusion constant, D =1.2+0.2X10 ' cm /sec, and a smoothly varying inelastic scattering spectrum with no indication of excitations of a molecular character. The FSDP remains well defined when the inelastic scattering is integrated over small energy transfers, indicating a lifetime of 10 ' sec or longer for the intermediate-range order responsible for this peak.

Ordering potential: the anomalous structure and properties of liquid KPb alloy

“…It is important to note that features are well represented by the present model. It is also worth mentioning here that theoretical model to describe the structure of liquid equiatomic KPb alloy was discussed by Reijers et al [8] on the basis of both random packing structural unit (RPSU) model and the reference interaction site model (RISM) ; the former model being originally developed by Powels and others [9] and latter one proposed by Chandler et al [10] for molecular liquids. In these models it is assumed that the system contains K 4 Pb 4 structural units in the equiatomic concentration.…”

La structure des liquides simples et des alliages liquides métalliques

“…Ces liquides, bien que formés de deux éléments dont le liquide pur est métallique, présentent pour certaines compositions des transitions électroniques avec une chute de la conductivité électrique. Pour ces mêmes compositions, leur facteur de structure total a une allure singulière avec en particulier un prépic intense qui ne peut être uniquement relié à Scc mais est aussi présent sur SNN Ceci peut être expliqué par la formation de complexes dans le liquide, similaires à ceux des phases solides, dû à un transfert de charge entre éléments chimiques aboutissant à des liaisons de nature ionique ou covalente [19,20,21]. Cependant, dans les liquides métalliques (mono-ou poly-atomiques) plus standards, l'ordre topologique n'a pas été examiné en détail à cause de la nature supposée isotrope des interactions inter-atomiques et de la difficulté de sa mise en évidence expérimentale.…”

Neutron Diffraction Investigation of Liquid Alkali Metal—Gallium Alloys. Giant Cluster Formation?

“…It is supposed, that the electronic structures of the liquid alloys resemble those of the solid counterparts which have saturated chemical bonds. The neutron diffraction patterns of the liquid alloys exhibit prepeaks associated with the long-range ordering caused by the formation of the Zintl ions (see, e.g., reference [4]). 1) While this work was in progress M. Alvarez and P. Verkerk died in a traffic accident.…”