The effect of addition of gallium on the thermal stability and crystallization kinetic parameters of GaxSe100-x glass system

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation for GaxSe100-x glass system (x=0, 2.5 and 5 at%). The kinetic parameters of GaxSe100-x glass system under non-isothermal conditions are analyzed by the model-free and model-fitting models at different constant heating rates (5-50 K/min). A strong heating rate dependence of the effective activation energy of crystallization was observed. The analysis of the present data shows that the effective activation energy of crystallization is not constant but varies with the degree of crystallization and with temperature as well. The crystallization mechanisms examined using the local Avrami exponents indicate that one mechanism (volume nucleation with one-dimensional growth) is responsible for the crystallization process for heating rates 5-50 K/min for Se glass and two mechanisms (volume nucleation with two- and one-dimensional growth) are working simultaneously during the amorphous-crystalline transformation of the Ga2.5Se97.5 and Ga5Se95 glasses (5-50 K/min). The reaction model that may describe crystallization process of all the compositions of GaxSe100-x glass system is Avrami-Erofeev model (g(α)=[-ln(1-α)]1/n) with n=2 for Se glass. While for Ga2.5Se97.5 and Ga5Se95 glasses, the values of n are equal to 3 and 2 for the heating rates 5-20 and 35-50 K/min, respectively. A good agreement between the experimental and the reconstructed (α-T) curves has been achieved. The transformation from amorphous to crystalline phase in GaxSe100-x glass system demonstrates complex multi-step involving several processes.