An alternative method for analyzing the non-isothermal glass-crystal transformation kinetics: Application to the crystallization of some alloys of Ge-Sb-Se and Sb-As-Se glassy systems

A method has been developed for analyzing the non-isothermal glass-crystal transformation kinetics in materials for which the nucleation process takes place early in the transformation and the nucleation frequency is zero thereafter, the condition of “site saturation”. Under this condition the Johnson–Mehl–Avrami transformation rate equation can be rigorously applied at non-isothermal processes. Considering the assumptions of extended volume and random nucleation, a general expression of the fraction transformed as a function of time in isothermal crystallization processes has been obtained. The application of the quoted expression to non-isothermal transformations has been carried out under the above-mentioned condition of “site saturation”. Thus, the alternative method developed, starting from Johnson–Mehl–Avrami equation, initially equals two values of the volume fraction transformed, corresponding to two constant heating rates in different times, to deduce the activation energy of the transformation. Next, the kinetic exponent is obtained combining two transformed fractions, corresponding to two different values of the time in a single-scan. The theoretical method developed has been applied to the crystallization kinetics of some semiconducting alloys, prepared in our laboratory, corresponding to the Ge-Sb-Se and Sb-As-Se glassy systems, and which fulfil the condition of “site saturation”. The obtained values for the kinetic parameters satisfactorily agree with the calculated results by the non-isothermal technique of multiple-scan. This fact confirms the reliability and accuracy of the theoretical model developed.