Microstructural characterization and crystallization kinetics of (1-x)TeO2-0.10CdF2-xPbF2 (x = 0.05, 0.10, and 0.15 mol) glasses

Microstructural characterization and crystallization kinetics of (1-x)TeO2-0.10CdF2-xPbF2 (x = 0.05, 0.10, and 0.15 in molar ratio) glasses were investigated using differential thermal analysis (DTA), x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy/energy dispersive spectrometer (SEM/EDS), and absorbance spectroscopy techniques. For all of the glass compositions only one exothermic peak was observed on the DTA plots, and on the basis of the XRD and Raman spectrophotometry investigations it was understood that they refer to the formation of the α-TeO2 phase. SEM/EDS investigations revealed the presence of oriented needle-like α-TeO2 crystals in the 0.85TeO2-0.10CdF2-0.05PbF2 glass, rectangle-shaped α-TeO2 crystals in the 0.80TeO2-0.10CdF2-0.10PbF2 glass, and disoriented needle-like crystals in the 0.75TeO2-0.10CdF2-0.15PbF2 glass. DTA analyses were carried out at different heating rates, and the Avrami constants for all of the glasses were approximately 1. The activation energy calculations and SEM investigations demonstrated that the formation of the crystalline phases occurred via surface crystallization mechanism for all of the glasses. Activation energies for crystallization in these glasses were determined from the modified Kissinger plots and were found to vary between 67 and 183 kJ/mol. The addition of PbF2 as a network modifier into the glass structure contributes to the intensity of the Raman peaks change and forced the transition of the glass network from TeO4 trigonal bipyramid units to the TeO3 trigonal pyramid structural units.