Microstructural characterization and crystallization kinetics of (1 − x)TeO 2– xK 2O ( x = 0.05, 0.10, 0.15, 0.20 mol) glasses

Abstract

Microstructural characterization and crystallization kinetics of (1 − x)TeO 2– xK 2O ( x = 0.05, 0.10, 0.15, and 0.20 in molar ratio) glasses were investigated using DTA, XRD, Raman spectroscopy, optical microscopy and SEM techniques. Whereas only one exothermic peak was observed for the 0.95TeO 2–0.05K 2O and 0.90TeO 2–0.10K 2O glasses, two crystallization peaks were present on the DTA plots of the 0.85TeO 2–0.15K 2O and 0.80TeO 2–0.20K 2O glasses. On the basis of the XRD and Raman spectrophometry investigations, α-TeO 2, γ-TeO 2 and K 2Te 4O 9 crystal phases were present in the (1 − x)TeO 2– xK 2O ( x = 0.05, 0.10, 0.15, and 0.20 in molar ratio) glass samples heated above the peak crystallization temperatures, T p. SEM/EDS investigations of (1 − x)TeO 2– xK 2O ( x = 0.05, 0.10, 0.15, and 0.20 in molar ratio) glasses heated above T p revealed the presence of distinct TeO 2-rich and K 2Te 4O 9 in the 0.95TeO 2–0.05K 2O and triangular wedge-shaped crystalline regions in the 0.90TeO 2–0.10K 2O, 0.85TeO 2–0.15K 2O and 0.80TeO 2–0.20K 2O glasses. DTA analyses were carried out at different heating rates and the Avrami constant for the 0.95TeO 2–0.05K 2O glass was calculated as 0.94, an indication of surface crystallization also confirming SEM results. On the other hand, the n values were between 1.7 and 1.87 for the exothermic peaks of the 0.80TeO 2–0.10K 2O, 0.85TeO 2–0.15K 2O and 0.80TeO 2–0.20K 2O glasses, indicating one-dimensional crystalline growth mechanisms for these glasses. Activation energies for one-dimensional crystal growth mechanisms in these crystals determined from the modified Kissinger plots were found to vary between 550 and 650 kJ/mol.