Thermodynamic properties of liquid Rb-Pb alloys

Thermodynamic properties of liquid Rb-Pb alloys are deduced from electromotive force measurements using a coulometric titration technique. From a combination of measurements as a function of composition or temperature. Gibbs energies of mixing, entropies of mixing, and excess heat capacities are derived for alloy compositions covering the range from pure lead to 70 at.% Rb. At the equiatomic composition, extrema are obtained in the variations with composition of the Darken excess stability, the entropy, and the excess heat capacity. Recent electrical resistivity, calorimetric, and neutron diffraction measurements indicated an unusual behaviour at the same composition, which was interpreted in terms of polyanionic species. The present results corroborate the presence of structural units that become predominant at the equiatomic composition. A departure from this composition through addition of Rb or Pb leads to a decrease and dissociation of these species into free atoms.