In DSC plots for chalcogenide glasses, the heat flow has positive value and increases with temperature. With heavy doping of foreign atom in chalcogenide glasses, the plots shows negative values of heat flow. What may be the reason for negative heat flow? Or what is the meaning of this type of changes?
As Dr. Sakthidharan said, you could have a phase change, if the impurities are their own phase. Alternatively, the heavily doped glass could be unstable and crystallizing. When you see heat flow drop during a temperature increase, try holding a constant T and seeing if the heat is still negative.
Dear Dr. Sakthi Dharan, Pb has been doped in IV-VI semiconductor. Pure as well as Pb-doped materials, all undergo a phase transition from amorphous to crystalline phase and there is peak in all compositions studied. The negative values of heat flow are or may be due to reference pan in DSC. But question is for Heat flow why it is increasing with temperature for pure sample, then with small Pb-doping, change in heat flow with temperature decreases. With some more Pb-doping, heat flow starts to decrease with temperature.
Dear Dr. Pavel Mardilovich, samples have been characterized for DSC from somewhere else not in my lab so repeating it is somehow unmanageable. With doping, glass may be unstable, that may be the reason, for decreasing heat flow with temperature?
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