The ion transport properties of soda-lime silicate and alkali borate glasses were studied with complimentary tracer diffusion and impedance spectroscopy techniques in order to investigate the ion dynamics and mixed-alkali effect. In soda-lime silicate glasses the tracer diffusivity of 22Na alkali ions was more than six orders of magnitude faster than the diffusivity of earth alkali 45Ca ions. This observation was attributed to a stronger binding of bivalent earth alkali ions to the glass network as compared to that of alkali ions. The conductivity of the investigated standard soda-lime silicate glasses was mostly due to the high mobility of sodium ions and a temperature independent Haven ratio of about 0.45 was obtained. For single alkali sodium-borate glasses, the Haven ratio was also temperature independent, however, it was decreased with decreasing temperature for rubidium-borate glass. The mixed-alkali effect was investigated for Na-Rb borate glasses and it was observed that the tracer diffusivities of 22Na and 86Rb ions cross, when plotted as function of the relative alkali content. This crossover occurred near the Na/(Na+Rb) ratio of the conductivity minimum due to mixed-alkali effect. The authors suggest that this crossover and the trend of diffusion coefficients was the key to an understanding of the mixed-alkali effect.

Diffusion and Ionic Conduction in Oxide Glasses. H.Mehrer, A.W.Imre, E.Tanguep-Nijokep: Journal of Physics - Conference Series, 2008, 106[1], 012001 (9pp)