Structural modifications induced by Na+/K+ ion exchange in silicate glasses: A multinuclear NMR spectroscopic study

The structural mechanisms of stress relaxation during Na+/K+ ion exchange is studied in a variety of Na silicate glasses with and without alkaline-earth modifiers, using one and two-dimensional 23Na and 29Si nuclear magnetic resonance (NMR) spectroscopy. The results suggest that significant structural modifications accompany the Na+/K+ ion exchange process in the form of a shortening of the average Na[sbnd]O and Si[sbnd]NBO distances and an opening of the Si[sbnd]O[sbnd]Si angles without any detectable change in the Qn speciation. These trends are similar to those observed in analogous mixed Na,K glasses derived via the melt-quench route, with increasing K:Na ratio. Consequently, the ion-exchange-induced reorganization of the glass network is accompanied by a partial relaxation of the stress generated by the exchange of smaller Na+ by the larger K+ and better accommodation of the latter ion as a modifier.SCOPUS: ar.j