Self-Diffusion of Sodium in Sodium Chloride and Sodium Bromide

Abstract

The self-diffusion coefficient of sodium in sodium chloride and sodium bromide has been measured as a function of temperature. A comparison of the self-diffusion coefficient with the electrolytic conductivity reveals that the Einstein relation is satisfied at high but not at low temperatures. The temperature dependence of the diffusion coefficient may be explained by the Schottky-Wagner vacancy theory if the presence of impurity ions is taken into account. A possible explanation for the failure of the Einstein relation in terms of association between multivalent foreign ions and vacancies is suggested.