A study on the glass-crystal transformation under non-isothermal regime: Evaluation of the crystallization kinetics of the Ag_(0.24)As_(0.30)Se_(0.46) http://Ago.24Aso.30Seo.4e glassy semiconductor by using the theoretical method developed (TMD) and a model-fitting approach

摘要

This work analyzes the glass-crystal transformation kinetics of the Ag_(0.24)As_(0.30)Se_(0.46) glassy alloy, which presents two exothermic peaks, using differential scanning calorimetry (DSC) technique under non-isothermal conditions. The corresponding kinetic parameters are evaluated considering two different methods. On the one hand, the theoretical method developed (TMD), which we have published in two previous articles. This method allows one to calculate the quoted parameters, to establish the thermal process type, to determine the dimensionality of the crystal growth and to evaluate the separate activation energies for the nucleation and for the growth, as well as, the exponents of the power laws of the time-dependence for the nucleation frequency and for the crystal growth rate in the crystallization of the quoted alloy. The value of the kinetic exponent for the second peak is quite larger than 4, which can be justified considering the TMD's hypotheses. The thermal processes identified in this alloy are glass-crystal transformations, with continuous nucleation and one-dimensional growth for the first peak, and with "site saturation" and three-dimensional growth for the second peak. On the other hand, in order to obtain information about the variation of the activation energy of each peak with the transformed fraction and, accordingly, with the temperature, the experimental data of the above-mentioned alloy have been analyzed using a model-fitting approach. Thus, the variation of the activation energy for both peaks with the transformed fraction demonstrates that the rate constant of the transformation is in fact determined by the rates of two processes, nucleation and diffusion, which resulting in varying the activation energy of the transformation with the temperature. The obtained results for the transformation kinetic parameters, using the already quoted two methods under non-isothermal regime show a good agreement, which indicates the reliability of both methods to analyze the transformation kinetics of the quoted glassy alloy.