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 glassy semiconductor by using the theoretical method developed (TMD) and a model-fitting approach J.L. Cárdenas-Leal, J. Vázquez ⇑ , D. García-G. Barreda, P.L. López-Alemany, R. González-Palma, P. Villares Departamento de Física de la Materia Condensada, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, 11510 Puerto Real (Cádiz), Spain article info Article history: Received 4 July 2012 Received in revised form 25 July 2012 Accepted 27 July 2012 Available online 4 August 2012 Keywords: Glassy semiconductor Glass–crystal transformation Differential scanning calorimetry Dimensionality of the crystal growth Power law abstract 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-iso- thermal 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 ther- mal 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 crystalliza- tion 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 trans- formed 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 transfor- mation 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 kinet- ics of the quoted glassy alloy. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The solids that are not crystals and, in particular, the glassy sol- ids constitute one of the most active fields of solid-state study due to their unique isotropic, structural and chemical properties [1]. These materials have an important practical or potential applica- tion in various industrial areas [2]. Thus, the thermal stability of glassy systems can be related to their resistance to crystallization. The occurrence of crystallization during the heating of the quoted systems is of special importance from the aspect of both funda- mental research and application of these materials. Transparent chalcogenide semiconductors intended for use in microelectronics, optical memory, holography, diffraction optics and the like, must be thermally stable at room temperature. Very large variations of the essential characteristics of photochromic glasses are achieved by introducing Ag, Cu or Cd into the chalcogenide systems [3,4]. In this sense, the advances that have been made in physics and chemistry of the non-crystalline solids, in general, have been widely appreciated within the research community. It is well know that the solid-state phase transformations play an important role in the industrial production. Therefore, a great impulse has been given at the study of a general description of the kinetics of phase transformation [5], and accordingly, the last 50 years have seen a strong theoretical and practical interest in the application of calo- rimetric analysis techniques to the study of the quoted transforma- tions [6–8]. Thus, the classical theory of nucleation and crystal growth has been developed over the last 60 years. A full develop- ment of the theory is given by Christian [9] and a noteworthy re- view published by Kelton [10]. 0925-8388/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2012.07.139 ⇑ Corresponding author. E-mail address: jose.vazquez@uca.es (J. Vázquez). Journal of Alloys and Compounds 544 (2012) 188–196 Contents lists available at SciVerse ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom