Internal Friction in L.A.S. Type Glass and Glass-Ceramics

Internal friction measurements have been performed on glass and glass-ceramics of the Li2O-Al2O3-SiO2 type by isothermal mechanical spectroscopy. Experiments were carried out over a large frequency range (10-4Hz - 31.6 Hz) for various temperatures between 260K and 850K. For the glass, a relaxation peak is observed at low temperature (276K for 1Hz). This peak does not appear in the glass-ceramics ; however, for each of them, two other peaks were observed : the first one at about 343K (1Hz) and the second one at higher temperature, between 600K et 700K (1Hz). Our dielectric loss investigation data obtained on the same materials have allowed to assume that the low-temperature peaks are due to the stress-induced diffusion of Li+ ions, in the vitreous phase for the glass and in the crystal phase for the glass-ceramics respectively. The peaks observed at higher temperature in glass-ceramics depend on the crystal phase but the relaxation mechanisms responsible of them are not well defined.