Ordering potential in liquid Li4Pb and Li7Ag3calculated from neutron diffraction data

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Abstract
SCC(q) data obtained by neutron diffraction at different temperatures for liquid Li4Pb and Li7Ag3 are used to calculate curves for W(r) which, according to Copestake et al. (1982, 1984) correspond approximately to the ordering potential V(r) at distances r larger than the hard-core diameter sigma . The authors find further support for this assumption from the fact that for liquid Li4Pb the ordering enthalpy Delta Hord introduced by Hafner et al. (1984), calculated from W(r) and the Fourier transform of SCC(q), is almost identical to the value given by Hafner et al., as it should be if W(r> sigma ) are really identical to V(r> sigma ). The diffraction data also yield meaningful values for the temperature derivative of Delta Hord. In all cases, the decreasing part of mod W(r> sigma ) mod behaves similarly to a Yukawa potential Wy(r). If the effective interatomic interaction is assumed to arise from a positive charge at the Li site and a corresponding negative charge at the site of the other component, and if the electron screening is treated with the help of local pseudopotentials and the Thomas-Fermi approximation, the authors find that the amount of charge transfer in the two alloys is approximately the same and varies only a little with temperature. The electronic screening, however, is much stronger in Li7Ag3 than in Li4Pb and increases significantly with temperature for the latter.