Metal-non-metal transition in liquid alloys with polyvalent components

Abstract

The metal-non-metal transitions that occur in certain alloy systems as a function of concentration have been investigated in three alloys that have polyvalent components, using a calculational model that was applied previously to the gold-alkali alloys. The important elements of the model, charge transfer and local chemical order, are treated self-consistently and the equilibrium state of the system is found by minimising the free energy. It is found that the transitions predicted by the model agree well with a variety of experimental results. The Cs-Sb and Na-Sb systems are found to have a high degree of local chemical order and a charge transfer of about 25 electrons per atom in the concentration region near stoichiometry where the transitions occur. At other concentrations the alloys are found to be random and the charge transfer drops to about 1/4 electron per atom. For the Li-Pb system, which is known to remain metallic for all concentrations, an intermediate degree of local order and charge transfer of about 1.5 electrons per atom appear to be consistent with experimental results in the concentration region near stoichiometry. Differences between these alloys and the gold-alkali systems are discussed.