Glass transformation studies in Ge-Se-Bi system
The thermal behavior of bulk glasses in the Ge20Se80 − xBix(x = 2.5, 4.0, 6.0 at %) system is studied using modulated differential scanning calorimetry (MDSC). All samples have the same thermal history as a result of heating to a temperature above the glass transition point, equilibrating, and then cooling. The total heat flow, modulated heat flow, reversing heat flow, and nonreversing heat flow under heating and cooling schedules are measured. The glass transition temperature Tg, the relaxation enthalpy ΔH, the specific capacity Cp, and the specific heat capacity difference ΔCp = Cpl − Cpg, which characterize the thermal events in the glass transition region, are also determined. These parameters reveal an increase with x, which can be attributed to the increase in the average coordination number with an increase in the bismuth content (at %) in the composite. The ratio of heat capacities Cpl/Cpg, the width of the glass transition temperature range ΔTg, and the activation enthalpy for glass transition ΔHTg are also studied. The values of the ratio Cpl/Cpg vary in the range between 1.038 and 1.112. The activation energy of crystallization is evaluated using the Kissinger, modified JMA, and Matusita equations, which is found to be in the range of 100.92 kJ/mol.
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