Chemical potentials and fluctuations in indium–iodine solutions

Abstract

The composition dependence of the relative chemical potential of In in liquid In–I alloys was determined from emf data obtained over the range of composition from In to InI3. Electrical conductivities were also measured for a limited number of concentrations. The specific conductance of the InI3 composition differs from that of pure liquid In by almost five orders of magnitude; i.e., at 600 °C that for InI3 is 0.104 while that for the pure metal is 2.16 × 104 Ω−1cm−1. At the long-wavelength limit the concentration correlation function Scc(0), which was calculated from the chemical potential data, exhibits large composition fluctuations on the In-rich side and minimal compositional disorders in the vicinity of the intermediate compositions InI, InI2, and InI3. The mean square compositional fluctuation is developed to discuss the crude short range ordering, ΔNα and the role of charge transfer, Δeα, in a general statistical mechanical theory of solutions. The large peak in Scc(0) at the indium-rich side provides crucial evidence of large concentration fluctuations, accompanied by microscopic inhomogeneities in the electronic structure, if a bimodal distribution is assumed. The limit ΔNα → 1 near the InI, InI2, and InI3 compositions shows that a preference exists for unlike nearest neighbors because of the ionic or covalent character in the chemical bonding. It is proposed that over the In-InI range there is the relationship between a gradual metal–nonmetal transition and the large concentration fluctuations which are associated with microscopic inhomogeneities in the electronic structure.