Evidence from infrared spectroscopy of structural relaxation during field assisted and chemically driven ion exchange in soda–lime–silica glasses

Evidence is provided by infrared reflectance spectroscopy of structural relaxation occurring in ion exchanged surface layers in commercial soda–lime–silica glasses. Monovalent cations (K⁺, Ag⁺ and Li⁺) are introduced from molten nitrate baths both by simple diffusion and with the assistance of externally applied electric fields. In the case of K⁺ ions, a highly resistive layer is created and is characterised by impedance spectroscopy. The mid infrared spectra provide information on changes in the silicate network: they show that the introduction of Li⁺ and Ag⁺ leads to a disproportionation reaction with conversion of Q₃ into Q₂ and Q₄ species. In contrast, the introduction of K⁺ ions leads to the opposite (i.e. comproportionation) reaction, where Q₂ and Q₄ are converted into Q₃ units. These processes are chemically driven; they are impeded, e.g. by the build up of internal pressures accompanying the introduction of the larger K⁺ ion. The results provide direct evidence for cation-induced relaxations in the glass network (CAIRON).