Microstructural characterization and crystallization kinetics of (1- x )TeO 2 -0.10CdF 2 - x PbF 2 ( x = 0.05, 0.10, and
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zen Gonul O Department of Physics, Faculty of Science and Letters, Istanbul Technical University, Maslak 34469 Istanbul, Turkey
Scott A. Speakman Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 14 November 2008; accepted 25 March 2009)
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 a-TeO2 phase. SEM/EDS investigations revealed the presence of oriented needle-like a-TeO2 crystals in the 0.85TeO2-0.10CdF2-0.05PbF2 glass, rectangleshaped a-TeO2 crystals in the 0.80TeO2-0.10CdF2-0.10PbF2 glass, and disoriented needlelike 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 which refers to one-dimensional crystallization. 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.
I. INTRODUCTION
New glasses that promise novel properties such as a higher light regulation, extraordinary strength, or excellent heat and chemical durability are of interest to many scientists in the fields of applied physics, multimedia, optoelectronics, and energy development. Tellurite glasses, which have wide range of unique properties, have possible applications in pressure sensors, as new laser hosts, or in different applications such as new materials for second-harmonicgeneration, third-order-nonlinear optical materials, up-convention glasses, optical switches, and optical amplifiers.1 The glass-forming regions, crystallizing tendencies, and density and thermal-expansion coefficients of different multicomponent oxyhalide tellurite glasses have been studied by different groups.1 In addition, it was later a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0380 J. Mater. Res., Vol. 24, No. 10, Oct 2009
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understood that the contribution of the heavy metal ions into the oxide systems increased the absorption ability, and the refractive in
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