Crystallization Studies on Se-Te-Cd Chalcogenide Glasses

Abstract

The thermal crystallization behavior of bulk Se90� xTe10Cdx (x ¼ 0, 3, 9, and 15 at%) glasses was studied by differential thermal analysis, (DTA), under non-isothermal conditions. The glass transition temperature, (Tg), the onset crystallization temperature, (Tc), and the peak temperature of crystallization, (Tp), were found to be dependent on both the composition and the heating rates. From the dependence on the heating rates (� )o f (Tg) and (Tp), the activation energy for the glass transition, (Et), and the activation energy for crystallization, (Ec), were calculated and their composition dependence is discussed. The crystalline phases resulting from DTA and scanning electron microscopy (SEM) have been identified using X-ray diffraction. The results indicate one dimensional growth from the surface to the inside for all the studied compositions. The kinetic parameters determined have made it possible to discuss the glass forming ability. (doi:10.2320/matertrans.MC200928) The study of the crystallization kinetics of a glass upon heating can be undertaken in several different ways. In calorimetric measurements two techniques have been em- ployed for the study of the crystallization behavior upon heating, namely isothermal and non-isothermal crystalliza- tion analyses. 6,7) In the isothermal method, the sample is brought quickly to a temperature above the glass transition temperature, Tg, and the heat evolved during the crystalliza- tion process at a constant temperature is recorded as a function of time. In the other method, the sample is heated from room temperature, at a fixed heating rate (� ), and the heat evolved is again recorded as a function of temperature. The present work is concerned with the study of the crystallization kinetics and the evaluation of the crystalliza- tion parameters for Se90� xTe10Cdx (x ¼ 0, 3, 9 and 15 at%) chalcogenide glasses by using the non-isothermal method. The effect of composition on the crystallization mechanism has been reported. 2. Experimental The bulk materials of Se90� xTe10Cdx (x ¼ 0, 3, 9 and 15 at%) were prepared by the usual melt quench technique; the highly pure materials (99.999%) were weighted accord- ing to their percentages and sealed in evacuated silica tubes which were heated at 900 � C for 20 h. During the melt process the tube was frequently rocked to intermix the constituents and to increase homogenization of the liquid. This treatment was followed by quenching in an ice/water mixture. The amorphous nature of the sample was proved by X-ray diffraction. Differential Thermal Analyses (DTA) was carried out by using a DTA Perkin-Elmer DTG-60 under non-isothermal conditions. The glass transition temperatures (Tg), the onset crystal- lization temperatures (Tc), and the peak crystallization temperatures (Tp), were determined with an accuracy of � 1 K using the microprocessor of a thermal analyzer. The crystallized fraction (� ) was calculated using the partial area analysis. For scanning electron microscopy (SEM) examina- tion, sample surfaces were etched using a mixed solution of sodium hydroxide and hydrogen peroxide. The X-ray diffractometer, Philips type 1710, was used to identify the crystalline phases in the annealed glassy samples.