Relaxation mechanisms and microstructure in glass and glass-ceramics

Abstract

Two LAS (Li 2O–Al 2O 3–SiO 2)-type glass-ceramics and their parent glass have been studied by isothermal mechanical spectroscopy. These materials have the same chemical composition but the two glass-ceramics differ in microstructure: one is a ‘β-quartz’ glass-ceramic whereas the other one is of ‘β-spodumene’ type. The isothermal internal friction measurements performed in a frequency sweep [10 −4–31.6 Hz] with an inverted torsion pendulum, submitted to subresonant forced oscillations, at temperatures between 93 and 820 K, have revealed several mechanical relaxation peaks. A single internal friction peak is observed in the glass sample whereas two peaks occur in the ‘β-quartz’ and ‘β-spodumene’ glass-ceramics. A detailed microstructure analysis (XRD, IRTF, SEM, TEM and DTA) and dielectric loss measurements have allowed to interpret these relaxation phenomena. The mechanical relaxation peak observed in the glass (∼290 K for 1 Hz) is assigned to the stress-induced movement of lithium ions. In each glass-ceramic the ‘low-temperature’ peak (∼340 K for 1 Hz) is linked with the ion mobility in the respective main crystalline phase. As for the ‘high-temperature’ peak, its origin is totally different for the two glass-ceramics; in the ‘β-quartz’ glass-ceramic it is due to the Mg 2+ and Zn 2+ 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.