Thermal analysis and physical properties of Bi–Se–Te chalcogenide glasses K.A. Aly a,b,⇑ , Farid M. Abdel Rahim a,b , A. Dahshan c,d a Physics Department, Faculty of Science and Arts, King Abdulaziz University (KAU), P.O. Box 80200, 21589 Khulais, Saudi Arabia b Physics Department, Faculty of Science Branch Assiut, Al Azhar University, Assuit, Egypt c Physics Department, Faculty of Girls, King Khalid University, Abha, Saudi Arabia d Physics Department, Faculty of Science, Port Said University, Port Said, Egypt article info Article history: Received 30 October 2013 Received in revised form 24 November 2013 Accepted 9 January 2014 Available online 18 January 2014 Keywords: Chalcogenide glasses Glass transition Thermal stability Crystallization kinetics abstract The present work reported the effect of variation of bismuth content on the glass transition, thermal stability and crystallization kinetics of Bi x (Se 20 Te 80 ) 100x (0 6 x 6 12) glasses. Measurements of the heat flow as a function of temperatures and different heating rates (b) for Bi x (Se 20 Te 80 ) 100x glasses were car- ried out by using differential scanning calorimetry (DSC). Both the heating rate and Bi content are found to affect the values of the characteristic temperatures such as the glass transition temperature (T g ), the peak temperature of crystallization (T p ) and the melting temperature (T m ). From the heating rate depen- dence of T g and T p , values of the activation energy for glass transition (E g ) and for crystallization (E c ) were deduced. Afify’s method was used to derive the values of E c without any dependence on the kinetic expo- nent (n). The compositional dependence of E g and E c was discussed in terms of the chemical bond approach. Based on the values of T g , T p , T m and E c the thermal stability criteria (DT, H r , H g , S, K(T) and K r (T)) of the studied glasses was evaluated. It was found that, increasing the Bi additions leads the decrease of the glass thermal stability i.e. the glass without any Bi content is the most stable one. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Chalcogenide glasses are becoming more and more popular due to their applications as infrared optical fibers, reversible phase change optical recording etc. [1]. Among the various chalcogenide glasses, Se–Te based alloys are preferred because of their higher photosensitivity, greater hardness, higher crystallization tempera- ture (T p ) and smaller aging effects as compared to pure selenium [2–5]. The addition of a third element like Sb, Sn, In, Pb and Bi has large effect on their structural, physical, optical, electronic and thermal properties [6–12]. Optical recording using a highly focused laser beam has recently made great progress in the area of high density of information stor- age. The performance of a re-writable phase change recording med- ium depends on: the sensitivity of amorphous to crystalline transformation, stability of both amorphous and crystalline states, and the reproducibility of the process. Although different phase change recording media were reported [13–15], the recording med- ia are expected to be further improved through the optimization of the materials. Like these materials must be shortly crystallization time and remains stable in the amorphous state as well as have been previously reported [16,17]. Therefore, it is very important to study the composition effect on the glass stability for recording materials. Presently it is hardly to formulate the composition dependence of the glass stability. In literature there are many suggested simple methods in order to evaluate the level of stability of the glasses. Most of these methods [18,19] are based on the characteristic tem- peratures (T g , T c , T p and T m ). In the present work the effect of Bi additions on the crystalliza- tion kinetics of (Se 20 Te 80 ) has been studied using calorimetric mea- surements under non-isothermal conditions. From the heating rate dependence of DSC thermograms, the activation energy for glass transition, the activation energy for crystallization and the kinetic exponent have been determined. Also the thermal stability factors and the glass-forming tendency of Bi x (Se 20 Te 80 ) 100x (x = 0, 4, 8 and 12 at.%) glasses have been investigated. 2. Experimental details Bi x (Se 20 Te 80 ) 100x (x = 0, 4, 8 and 12 at.%) chalcogenide glasses were prepared starting with their components of high purity (99.999%) by the usual melt quench technique. The proper amount (3 gm) for each sample was weighed according the atomic weight and the ratio of consistent elements, and then introduced into cleaned silica tubes of length 10 cm and width 1 cm. The tube was evacuated to http://dx.doi.org/10.1016/j.jallcom.2014.01.057 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Physics Department, Faculty of Science and Arts, King Abdulaziz University (KAU), P.O. Box 80200, 21589 Khulais, Saudi Arabia. E-mail addresses: kamalaly2001@gmail.com (K.A. Aly), adahshan73@gmail.com (A. Dahshan). Journal of Alloys and Compounds 593 (2014) 283–289 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom