Extended rigidity percolation and chemical thresholds in Ge–Te–Pb glasses as revealed by MDSC

Thermal analysis of Ge20Te80−xPbx (2≤x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures (Tc) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (ΔCpR), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (ΔHNR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system.