Abstract

Kinetic studies of two-phase transformations i.e. glass transition and crystallization for Ge_xSe₇₀Sb_30-x (x = 5, 10, 15, 20) glasses have been performed using differential scanning calorimetry (DSC) at different heating rates under non-isothermal condition. The glass transition and crystallization regions have been investigated in terms of their characteristic temperatures i.e. glass transition temperature T_g and crystallization temperature T_c and activation energy. The activation energies of glass transition and crystallization have been calculated by employing peak shift method of Kissinger and isoconversional methods. Activation energies have been found to be dependent on the composition. The thermal stabili- ty is determined from the temperature difference ΔT = T_c — T_g where T_c and T_g are the onset crystallization and glass transition temperature respectively. It has been found that Ge₁₅Se₇₀Sb₁₅ glass is thermally more stable as compared to the other members of the series.

Keywords

Glass Transition Region; Differential Scanning Calorimetry; Activation Energy; Thermal Stability

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1. Introduction

Among amorphous semiconducting materials, chalcogenide glasses containing a large amount of chalcogen atoms sulphur, selinium and tellurium have drawn great attention because of their broad applications in technological field such as memory devices and fiber optics. Selinium is an attractive material in optical memory devices due to its uniqueness of reversible transformation [1]. But pure Se has certain disadvantages like short lifetime and low stability. To improve these parameters certain other elements are added [2]. The Ge-Se-Sb alloys have good glass formation ability over a wide compositional range. This makes them good candidates as arsenic free IR transparent materials [3,4]. The Ge-Se-Sb glasses are used for fabrication of optical components like IR lenses for their transparency in the 2 μm to 16 μm wavelength region [5-7]. The aim of the present paper is to analyze the dependence of characteristic temperatures T_g, T_c and the activation energy on heating rate as well as composition respectively. An effort has also been made to determine the thermal stability of Ge-Se-Sb glasses.

2. Experimental Details

High purity (99.999%) Germenium, Selinium and Antimony were weighed and the weighed materials are then introduced into clean quartz ampoules with appropriate atomic weight percentage. The contents of the ampoule were sealed in vaccum of 10⁻⁶ torr and then heated in furnace where temperature was raised at a rate of 3 - 4 K∙min⁻¹ up to 925˚C. The contents were kept around that temperature for 12 - 14 hours with continuous rotation to ensure the homogeneity of the sample. The melton sample was rapidly quenched in ice-cooled water to get glassy state. The ingot of so produced glassy samples were taken out of the ampoule by breaking the ampoule and then grinded gently in mortar and pestle to obtain powder form.

The glasses are amorphous material therefore amorphous nature of these samples was characterized by Xray diffraction pattern using Bragg-Brentano geometry on a Panalytical X’pert Diffractometer with a Cu Kα radiation source (1.5406 Å).

The calorimetric measurements were carried out using differential scanning calorimetery (Rigaku DSC-8230) with an accuracy of ±0.1 K. 10 mg powdered samples were crimped into aluminium pans and scanned at different (10, 15, 20, 25 and 30 K∙min⁻¹) heating rates.

3. Result and Discussion

Figure 1 shows the DSC thermograms of Ge_xSe₇₀Sb_30−x (x = 5, 10, 15, 20) chalcogenide glasses at a heating rate of 10 K∙min⁻¹. It has been observed that each thermogram except for Ge₂₀Se₇₀Sb₁₀ represents two well-defined peaks. The first one is endothermic peak correspon ding to the glass transition region and other is exothermic peak corresponding to crystallization region. Figure 2 shows the DSC thermograms of Ge₅Se₇₀Sb₂₅ with different heating rates (10, 15, 20, 25 and 30 K∙min⁻¹). It has been observed from Figure 2 that both glass transition and crystallization temperatures shift towards the higher temperature side with the increase of heating rate.

Conflicts of Interest

The authors declare no conflicts of interest.

References