Microstructural characterization and crystallization behaviour of (1-x)TeO2-xWO(3) (x=0. 15, 0.25, 0.3 mol) glasses

DTA, XRD and SEM investigations were conducted on the (1-x)TeO2-xWO3 glasses (where x=0.15, 0.25 and 0.3). Whereas the 0.75TeO(2)-0.25WO3 and 0.7TeO(2)-0.3WO(3)-lasses show no exothermic peaks, an indication of no crystallization in their glassy matrices, two crystallization peaks were observed on the DTA plot of the 0.85TeO(2)-0.15WO(3) glass. On the basis of the XRD measurements of the 0.85TeO(2)-0.15WO(3) glass saniplesheated to 510 degrees C and 550 degrees C (above the peak crystallization temperatures), alpha-FeO2 (paratellurite), gamma-TeO2 and WO3 phases weredetected in the sample heated to 510 degrees C and the alpha-TeO2 and WO3 phases were present in the sample heated to 550 degrees C. SEM micrographs taken from the 0.85TeO(2)-0.15WO(3) glass heated to 550 degrees C showed that centrosymmetrical crystals were formed as a result of surface crystallization and were between 3 mu m and 15 mu m in width and 12 mu m and 30 mu m in length. On the other hand, SEM investigations of the 0.85TeO(2)-0.15WO(3) glass heated to 550 degrees C revealed the evidence of bulk massive crystallization resulting in lamellar crystals between 1 mu m and 3 mu m in width and 5 mu m and 30 mu m in length. DTA analyses were carried out at different heating rates and the Avrami constants for the 0.85TeO(2)-0.15WO(3)-lass heated to 510 degrees C and 550 degrees C were calculated as 1.2 and 3.9, respectively. Using the modified Kissinger equation, activation energies for crystallization were determined as 265.5 kJ/mol and 258.6 kJ/mol for the 0.85TeO(2)-0.15WO(3) glass heated to 510 degrees C and 550 degrees C, respectively. (c) 2005 Elsevier Ltd. All rights reserved.