Effect of Ion Size on Diffusion in Alkali Halides

Abstract

An experimental determination of the effect of ion size on diffusion has been made by measuring the diffusivity of ${\mathrm{Rb}}^{86}$ in NaCl, KCl, and RbCl. In the temperature region near the melting point the results follow the Arrhenius relation $D={D}_{0} \mathrm{exp}(\frac{\ensuremath{-}E}{\mathrm{kT}})$. The Arrhenius parameters are ${D}_{0}=205\ifmmode\pm\else\textpm\fi{}47,26.8\ifmmode\pm\else\textpm\fi{}8.7,33.3\ifmmode\pm\else\textpm\fi{}7.1$ ${\mathrm{cm}}^{2}$/sec and $E=2.11\ifmmode\pm\else\textpm\fi{}0.02,2.04\ifmmode\pm\else\textpm\fi{}0.03,1.99\ifmmode\pm\else\textpm\fi{}0.02$ eV for NaCl, KCl, and RbCl host crystals, respectively. We conclude that the effect of ion size is important with regard to both the frequency factor and activation energy. The results are in general agreement with the theory proposed in the previous paper.