Microstructural characterization and crystallization kinetics of (1−x)TeO2–xLiCl (x=0.6–0.4 mol) glasses

On the basis of DTA analyses, three (1−x)TeO2–xLiCl (x=0.3, 0.35 and 0.4 mol) glasses doped with 0.005 mol of Tm2O3 were crystallized in the vicinity of 400°C. X-ray investigations for samples heated to 425°C (above the peak crystallization temperature) followed by quenching in air, revealed the presence of the paratellurite (TeO2) as the only crystallizing phase in all glass compositions. SEM investigations revealed that the paratellurite crystals formed in these glasses as a result of surface crystallization were trigonal in shape, between 40 and 50 μm in length, 7 and 15 μm in width and 5 and 9 μm in depth. DTA analyses were carried out on the 0.7TeO2–0.3LiCl glass at different heating rates and an activation energy value of 238 kJ/mol for surface crystallization was determined graphically from a Kissinger-type plot using the analysis of Matusita and Sakka (Matusita, K. and Sakka, S., Kinetic study on crystallization of glass by differential thermal analysis — criterion on application of Kissinger plot. J. Non-cryst. Solids. 38&39, 741–746.).