Field-driven redistribution of “guest protons” within protonated silicate glasses

Protonated layers of lithium silicate glasses generated by electrolysis were penetrated by lithium ions from appropriate anodic solutions during a second electrolysis. As the electric fields were applied in the same direction during both electrolyses, the number of protons within the glasses was unchanged. As is made apparent in the discussions of the local resistivities and the resulting profiles of the electric fields within the electrolysed membranes, the steady state of the protonated layer was disturbed by the lithium ions making the migrating front of the less mobile protons unstable. The protons were diluted, while simultaneously the layer thickness was increased.

A remarkable change in the ir spectrum observed after the second electrolysis and indicating that Beer's law is not valid is explained by the tendency of protons to occupy preferred sites. It is proposed that mixed twin siloxy groups containing one lithium ion and one proton with different bond energies and thus different probabilities for leaving the entity act as proton traps and function as single sites for migrating lithium ions. The effect was observed with several lithium silicate glasses but not with a lithium aluminum silicate glass. Protons introduced as probes for alkali into glasses may thus contribute information on the glass structure.