Microstructural characterization and crystallization kinetics of (1-x)TeO2-xK(2)O(x=0.05, 0.10, 0.15, 0.20 mol) glasses

Microstructural characterization and crystallization kinetics of (1-x)TeO2-xK(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, alpha-TeO2, -gamma-TeO2 and K2Te4O9 crystal phases were present in the (1-x)TeO2-xK2O (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 (I - x)TeO2-xK2O (x = 0.05, 0.10, 0.15, and 0.20 in molar ratio) glasses heated above Tp revealed the presence of distinct TeO2-rich and K2Te4O9 in the 0.95TeO(2)-0.05K(2)O and triangular wedge-shaped crystalline regions in the 0.90TeO(2)-0. 10K(2)O, 0.85TeO2-0,15K(2)O and 0.80TeO(2)-0.20K2O glasses. DTA analyses were carried out at different heating rates and the Avrami constant for the 0.95TeO2-0.05K(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. (C) 2007 Published by Elsevier Ltd.