Published online by Cambridge University Press: 15 February 2011
Comprehensive studies using X-ray Absorption Fine Structure (XAFS) spectroscopy of the local environments in oxide glasses of alkalis like Na point to the existence of channels of modifying oxide within the glass forming network - a Modified Random Network or MRN. It has been proposed that these are the primary pathways for ionic conduction. Such microsegregation demands a high alkali coordination for non-bridging oxygens. This has now been confirmed from analysis of the O near edge XAFS of silica and sodium disilicate glass. Dielectric relaxation in oxide glasses provides considerable evidence for the cooperative action of alkali ions. The MRN has been used to develop specific microscopic models for ionic transport based on XAFS and incorporating correlated ionic movement. These quantitatively predict the ionic conductivity of silicate and aluminosilicate glasses and the compositional dependence of the activation energy with alkali concentration.