Electronic Processes in Solutions of Alkali Metals in Liquid Ammonia. II. Electrical Conductivity

Abstract

An attempt has been made to account for the electrical conductivity in sodium/liquid-ammonia solutions throughout the entire range of concentrations. The conductivity in dilute solutions is calculated from the Onsager—Kim theory, adjusted for the effective concentrations of conducting species. In the intermediate concentration range a conduction mechanism is proposed, according to which the conduction proceeds by the jumping of electrons from M centers to metal ions. In order to obtain the mobility, the system of the two nuclei and the electron is treated like a hydrogen molecule-ion immersed in a dielectric medium, and the jump frequency is calculated from the exchange integral appropriate for such a system. No arbitrary parameters are used in the theory. The calculated conductivity agrees well with the experimental data, from dilute solutions up to about 1M. The conductivity in concentrated solutions is calculated by assuming scattering of conduction electrons by screened metal ions. It is estimated that, although a narrow conduction band begins to form at concentrations of about 1M, the new structure is not complete, except at the highest concentrations. In order to account quantitatively for the observed conductivity above 1M, it is assumed that the conduction proceeds via a band formed by the overlap of wavefunctions in an excited level.