Spectroscopic and dielectric properties of a lithia-containing glass

Glass of the composition 65SiO2–20CaO–15Li2O (mol %) was prepared and subjected to heat treatment. The obtained samples were characterized before and after heat treatment by DTA, TG, XRD, SEM, IR and dielectric spectroscopy. DTA showed an endothermic peak at 954 °C, accompanied by a pronounced change in the microstructure, as revealed by SEM. XRD showed that metasilicate predominates on heat treatment at 726 °C, while on heat treatment at 726 °C, then at 954 °C, disilicate crystallizes as the main phase. The IR spectra of the heat-treated glasses revealed that the vibrations of O–H groups are drastically decreased, while those due to non-bridging oxygens Si–O− are increased. The dielectric constant (ε′), the loss tangent (tan δ) and the ac conductivity (σac) for the prepared glasses were investigated before and after heat treatment over a moderately wide range of frequency and temperature. The activation energy of the dielectric relaxation process was found to depend on the techniques of sample preparation. A drop of dielectric constant values was observed for the heat-treated sample, which can be attributed to the ordering of the induced crystalline phases. The conductivity behavior suggests a hopping mechanism responsible for conduction.