A model for the structure of liquid Li4Pb

Abstract

The authors present the results of calculations of the partial structure factors and radial distribution functions of liquid Li₄Pb at different temperatures. Assuming that this alloy is partially ionic, they have modelled the interionic forces by pairwise potentials that are strongly repulsive at small separations r and electronically screened Coulombic at large r. This model was motivated by the fact that an r-dependent ordering potential, which exhibits approximately screened Coulombic decay for larger r, can be extracted from the neutron diffraction data for S_CC(q) in Li₄Pb. The calculations, which are based on the mean-spherical and the hyper-netted-chain approximations, show that the wavenumber dependence of the measured concentration structure factor S_CC(q) can be reasonably well accounted for by the model with effective electron charges of about 0.5 and 4-2.0 at the Li and Pb sites, respectively, and an inverse screening length of 1.1 AA^-1. These parameters are consistent with values obtained from the ordering potential extracted from experiment. In order to explain the observed temperature dependence of S_CC(A) it is necessary to assume that the charge transfer between species decreases with increasing temperature.