Determination of activation energy of amorphous to crystalline transformation for Se 90 Te 10 using isoconversional methods N.M. Abdelazim ⁎, A.Y. Abdel-Latief, A.A. Abu-Sehly, M.A. Abdel-Rahim Physics Department, Faculty of Science, Assiut University, Assiut, Egypt abstract article info Article history: Received 31 August 2013 Received in revised form 1 January 2014 Available online 19 January 2014 Keyword: DSC; Crystallization kinetics; Chalcogenide glass; Activation energy; Isoconversional methods The activation energies of crystallization of Se 90 Te 10 glass were studied at different heating rates (4–50 K/min) under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The activation ener- gy was determined by analyzing the data using the Matusita et al. method. A strong heating rate dependence of the activation energy was observed. The variation of the activation energy was analyzed by the application of the three isoconversional methods, of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Vyazovkin. These methods confirm that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. This variation indicates that the transformation from amorphous to crystalline phase is a complex process involving different mechanisms of nucleation and growth. On the other hand, the validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for the studied composition was discussed. Results obtained by directly fitting the experimental DSC to the calculated DSC curve indicate that the crystallization process of the Se 90 Te 10 glass cannot be satisfactorily described by the JMA model. In general, simulation results indicate that the Sestak–Berggren (SB) model is more suitable to describe the crystallization kinetics. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Studies on amorphous chalcogenide glasses are of great interest due to their importance in preparing optical memories [1] and their optical applications are good for IR transmitting materials [2–4]. Moreover, they are interesting as core materials for optical fibers for transmission especially when short length and flexibility are required [5,6]. Many amorphous semiconducting glasses in particular selenium (Se) exhibit a unique property of reversible transformation [7]. The selection of Se is because of its wide commercial applications in xerography pho- tocell switching and memory devices etc. But its pure state has disad- vantages because of its short lifetime and low sensitivity. To overcome this difficulty, several workers [8–10] have used certain additives (Ge, Te, Bi, Zn etc.) to make binary alloys with selenium which in turn gives high sensitivity at high crystallization temperature and smaller aging effects. Recently, it has been pointed out that the Se–Te system based on Se has become materials of considerable commercial scientific and technological importance. They are widely used for various applications in many fields as optical recording media because of their excellent laser writer sensitivity xerography and electrographic applications such as photoreceptors in photocopying, laser printing infrared spectroscopy, and laser fiber techniques [11,12]. Furthermore, amor- phous Se–Te alloys have greater hardness, higher crystallization temperature, higher photosensitivity and smaller aging effects than pure Se [11]. Structural studies of chalcogenide glasses are important in deter- mining their transport mechanisms, thermal stability and practical ap- plications. Different techniques have been used to study the structure of chalcogenide glasses, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) [13–16]. The variation of the activation energy E with the degree of crystalli- zation is an important issue in the kinetics of amorphous to crystalline transformation. It can provide useful information about the different mechanisms involved in the transformation process as indicated by Vyazovkin [17]. Liu et al. [18] have considered a generalization of the Johnson–Mehl–Avrami (JMA) model to account the variation of the ac- tivation energy. In contrast to the original formalism of the JMA theory, where only nucleation site saturation or continuous nucleation was assumed, Liu et al. model predicts that the activation energy is not constant throughout the crystallization process when mixed nucleation (a combination of pre-existing nuclei and continuous nucleation modes, with site saturation and continuous nucleation as two extremes) is con- sidered. In order to reveal this variation of the activation energy of crys- tallization, two approaches are normally used. The first approach is to use the Matusita et al. [19] method to determine the kinetic parameters such as the activation energy E and the Avrami exponent n of the Journal of Non-Crystalline Solids 387 (2014) 79–85 ⁎ Corresponding author. E-mail address: nana841@hotmail.co.uk (N.M. Abdelazim). 0022-3093/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2014.01.012 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol