Theory of Molten Alkali Alloys. II. Na-K, Na-Rb, Na-Cs

Abstract

A previously described theory of the mixing properties of molten alkali metals is extended and used to investigate the sodium mixtures Na-K, Na-Rb, and Na-Cs at seven concentrations. Qualitatively it is found that a charge on the order of several hundredths of an electron is transferred, always from the larger to the smaller atom. Average distances between smaller atoms increase on mixing, while average distances between larger atoms decrease. This tendency is opposed by the change in Fermi energy and by changes in the Coulomb and exchange-correlation energies associated with the transfer of electrons from regions of relatively low charge density to regions of higher density. Calculated heats of mixing are found to agree reasonably well with experimentally measured values.