Mechanical relaxations in LAS-type glass and glass-ceramics related with microstructure

Abstract
Mechanical relaxation phenomena have been studied on two Li₂O-Al₂O₃-SiO₂-type glass-ceramics and their parent glass by isothermal mechanical spectrometry. These materials have the same chemical composition but the two glass-ceramics differ in microstructure : one is of "β-quartz" type whereas the other one is of "β-spodumene" type. The intemal friction measurements have shown several mechanical relaxation peaks. These relaxation effects have been interpreted from dielectric loss measurements and microstructure analysis (SEM, TEM, FTIR, XRD and DTA). For the glass, a single mechanical relaxation peak occurs : it is linked with the stress-induced movement of lithium ions. Contrary to the glass, two internal friction peaks are observed in the "β-quartz" and "β-spodumene" glass-ceramics. The low-temperature peak is assigned to the ion mobility in the respective main crystalline phase. For each glass-ceramic, the high-temperature peak is due to different relaxation mechanisms. In the "β-quartz" glass-ceramic, it is assigned to Mg²⁺ and Zn²⁺ion relaxation in the crystalline phase, whereas in the "β-spodumene" glass-ceramic, it is linked with a complex entity within the residual vitreous phase.