Alkali Ion Mobility in Mixed Cation Glasses (Part 1)

Abstract

In the system of 2RI2O⋅RII2O⋅7 SiO2 glasses (RI: Na, Cs and RII: Li, Na, K, Rb, Cs) the electrical coductivity in the temperature range of 150°-1200°C and the self-diffusion coefficient of RI ions at 600°C have been measured. The change in the mobility of the host alkali ion, RI, has been examined by introduction of various guest alkali ions, RII, The electrical conductivity and the self-diffusion coefficient of RI decreased with an increase in the difference in the ionic radii of RI and RII in a series with same RI. The dependence of alkali mobility on ionic sizes could be explained by the thermodynamics of molten alkali salt mixtures with a common anion. As the size parameter calculated from the theory on molten salt mixtures increased, the self-diffusion coefficients of RI decreased in the molten state of glass. It means that Coulombic repulsion force between the alkali ions as next-nearest neighbors tends to be more weak, the greater the difference in the both ionic radii. This lowering of the repulsion causes the mixed alkali effect. The results in the solid state of glass have been discussed from points of view for the binding force of alkali ions and the frozen temperature of glass mentioned in the previous reports.