Non-isothermal transformation of Pb-modified Ge-Se glasses

Abstract

Differential scanning calorimetric studies have been carried out on Ge_XSe_80-x Pb₂₀(17≤×≤24) bulk glasses, which exhibit a change from p- to n-type conduction at x=21at.%. All the samples show a single-stage crystallization followed by a single-stage glass transition. The dependence of glass transition temperature (T _g) on composition shows a maximum at x=21at.%. Structural relaxation around the glass transition has been studied by measuring T_g as a function of heating rate (β). Values of activation enthalpies (E _g) of the glass transition for different samples reveal that chemical bond breaking in the process of structural relaxation at T _g cannot be ignored. Crystallization kinetics have been analysed using the Kissinger method. The crystallization activation energy (E _c) and the frequency factor (C _o), calculated using the above method for different compositions, show anomalies at x=21 at.%. All the samples show the existence of two distinct melting points. The observed compositional dependence of T _g , E _c and C _o is discussed using the chemically ordered network model.