Dynamics of Network Formers and Modifiers in Mixed Cation Silicate Glasses

Abstract

Alkali / Alkaline-Earth / Silicate / Glasses / Network Formers / Network Modifiers / Self-Diffusion / Conductivity Conductivity measurements and diffusion studies with radioactive and stable isotopes were performed to investigate the diffusion of both network modifiers (alkali (A) and alkaline-earth (M) ions) and network formers (oxygen (O) and silicon (Si)) in various mixed-cation silicate glasses below the respective glass transition temperatures. The dynamics of the network modifiers A and M were studied in bulk glasses prepared from the melt and in sol-gel derived glass films. The diffusion anneals were performed under air and under reducing conditions in forming gas. No impact of the glass preparation on the diffusion of the network modifiers was found. However, the diffusion of the alkaline-earth ions is affected by additional defects formed under reducing conditions. The dynamics of the network formers O and Si was investigated against the type of alkali and alkaline-earth ions, their composition ratio, and the number of non-bridging oxygens. We found that Si diffusion is directly related to the rigidity of the glass. Combining the data on O diffusion with previous results on the diffusion of alkaline-earth ions M in glasses of the same composition, we conclude that the diffusion of O is likely assisted by M via the formation of O−M pairs.