Microstructural characterization and crystallization kinetics of (1−x)TeO2–xK2O (x=0.05, 0.10, 0.15, 0.20mol) glasses

Abstract

Abstract Microstructural characterization and crystallization kinetics of (1 − x )TeO 2 – x K 2 O ( 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 2 O and 0.90TeO 2 –0.10K 2 O glasses, two crystallization peaks were present on the DTA plots of the 0.85TeO 2 –0.15K 2 O and 0.80TeO 2 –0.20K 2 O glasses. On the basis of the XRD and Raman spectrophometry investigations, α-TeO 2 , γ-TeO 2 and K 2 Te 4 O 9 crystal phases were present in the (1 − x )TeO 2 – x K 2 O ( 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 – x K 2 O ( 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 2 Te 4 O 9 in the 0.95TeO 2 –0.05K 2 O and triangular wedge-shaped crystalline regions in the 0.90TeO 2 –0.10K 2 O, 0.85TeO 2 –0.15K 2 O and 0.80TeO 2 –0.20K 2 O glasses. DTA analyses were carried out at different heating rates and the Avrami constant for the 0.95TeO 2 –0.05K 2 O 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 2 O, 0.85TeO 2 –0.15K 2 O and 0.80TeO 2 –0.20K 2 O 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.