An investigation of the kinetic transformation mechanism of Ge12.5Te87.5 chalcogenide glass under non-isothermal regime

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation in Ge12.5Te87.5 chalcogenide glass. The kinetic parameters of glassy Ge12.5Te87.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (5–50 K/min). The effective activation energy of crystallization was determined by analyzing the data using the isoconversional methods of Kissinger–Akahira–Sunose (KAS), Tang, Starink, Flynn–Wall–Ozawa (FWO) and Vyazovkin. The analysis of the present data shows that the effective activation energy of crystallization is constant throughout the entire interval of conversions and hence with temperature. The transformation mechanism examined using the local Avrami exponents indicates that one mechanism (three-dimensional growth) is responsible for the transformation process for all heating rates used. The reaction model that may describe the transformation process of the Ge12.5Te87.5 chalcogenide glass is the Avrami–Erofeev model (g(α) = [− ln(1 − α)]1/n) with n = 3 for all heating range at the whole range of crystallized fraction (α = 0.05–0.95). A good agreement between the experimental and the reconstructed (α–T) curves has been achieved. The transformation from amorphous to crystalline phase in Ge12.5Te87.5 chalcogenide glass demonstrates a single-step mechanism.

Research highlights
► Thermal analysis using the DSC tool.
► The crystallization kinetics parameters.
► Isoconversional (model-free) methods.
► Model-fitting methods.
► The transformation mechanisms.