Self-diffusion of alkaline-earth ions in various mixed cation silicate glasses with

the composition, A2O·2MO·4SiO2, was investigated by performing radiotracer

diffusion measurements below the respective glass-transition temperatures.

Overall, the diffusivity of divalent ions was analyzed in mixed-cation systems with

A = Li, Na, K or Cs and M = Ca, Sr or Ba. The activation enthalpy depended

strongly upon the type of cation: revealing an increasing diffusivity for glasses with

cations of similar size. This behaviour was consistent with mechanical loss

spectroscopy measurements which were performed on the same glasses. Foreignatom

diffusion of calcium and barium in strontium-containing glasses was also

performed. In cases where the ionic radius of the alkali ion exceeded that of the

alkaline-earth ion, the diffusion activation enthalpy of the foreign ion equalled the

activation enthalpy for self-diffusion. The results could be described on the basis of

a theoretical model (Kirchheim, 2003) that related the activation enthalpy to

electrostatic and elastic contributions. Self- and Foreign Alkaline-Earth Diffusion in Mixed Cation Silicate Glasses.

F.V.Natrup, M.Grofmeier, H.Bracht: Solid State Ionics, 2009, 180[2-3], 109-15