Spin-Echo Double Resonance NMR Evidence for Preferential Like-Cation Clustering in Mixed-Alkali Disilicate Glasses

For the first time, spin-echo double resonance (SEDOR) nuclear magnetic resonance (NMR) spectroscopy has been applied to oxide glasses in a detailed structural study of the mixed-alkali effect. The use of a novel combination of the SEDOR NMR technique and computer simulations of different structural arrangements using molecular dynamics models has provided direct conclusive evidence for a preferential clustering of like cations in Na-Li disilicate glasses. This finding is in marked contrast with the stochastic mixing of cations or the formation of mixed-cation pairs proposed previously in the literature.