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 Q(3) into Q(2) and Q(4) species. In contrast, the introduction of K+ ions leads to the opposite (i.e. comproportionation) reaction, where Q(2) and Q(4) are converted into Q(3) 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).