Mousa M. A. Imran

Glass Transition Phenomena, Crystallization Kinetics and Enthalpy Released in Binary Se100–xInx (x = 2, 4 and 10) Semiconducting Glasses

Results of Differential Scanning Calorimetry (DSC) under non-isothermal conditions on Se 100-x In x (x = 2, 4 and 10) glasses are reported and discussed. The glass transition region has been investigated in terms of activation energy and the dependence of glass transition temperature Tg on coordination number with varying composition and heating rates. The crystallization kinetics and its dimensionality have been studied using two different models viz. Matusita and Ozawa equations. On the basis of the obtained experimental data the temperature difference T c - Tg and the enthalpy released, ΔH c , are found to be maximum and minimum, respectively, for Se 96 In 4 glass which indicate that this glass is the thermally most stable in the composition range of investigation.

Enthalpy recovery during structural relaxation of Se96In4 chalcogenide glass

Abstract Structural relaxation of isothermally and isochronally heat-treated Se 96 In 4 chalcogenide glass in the glass transition region has been studied using a differential scanning calorimeter (DSC). The recovery of excess enthalpy Δ H excess has been calculated from the knowledge of excess apparent specific heat Δ C p ,a ( T ) and plotted as a function of annealing time t a . Δ H excess has been found to vary with t a ; this variation follows a power-law behaviour and an expression of the form Δ H excess =Δ H o [ t a ] y has been proposed to describe such variation . Following the Kissinger formalism the activation energy of structural relaxation E t , both for annealed and un-annealed samples, has been obtained. The so obtained values of structural relaxation activation energies are indicative of the fact that some kind of bond interchange has taken place which in turn accounts for the relaxation process in Se 96 In 4 glass. From the knowledge of Δ H excess ( T a , t a ) and the corresponding activation energy, the activation energy spectra have also been drawn and discussed.

Glass transition phenomena, crystallization kinetics and thermodynamic properties of ternary Se80Te20−xInx (x=2, 4, 6, 8 and 10) semiconducting glasses: theoretical and experimental aspects

Abstract This paper presents the results of kinematical studies of glass transition and crystallization in glassy Se 80 Te 20− x In x ( x =2,4, 6, 8 and 10) using differential scanning calorimetry (DSC). Also the thermodynamic properties of these glasses in the transformation range of temperatures have been studied. Glass transition region has been investigated in terms of activation energy, dependence of glass transition temperature on coordination number with the varying composition and heating rates. The growth kinetics and its dimensionality have been investigated using three different models viz. Kissinger, Ozawa and Matusita equations. On the basis of the obtained experimental results on phase transformations in these glasses, thermodynamic parameters like entropy difference between metastable states in the glassy region, difference of Gibbs free energy, specific heat, entropy between the two phases and the enthalpy released during crystallization have been determined. On the basis of experimental observations and theoretical calculations of thermodynamic properties, it has been found that Se 80 Te 10 In 10 is the most stable glass.

Kinetic studies of bulk Ge22Se78-xBix (x=0, 4 and 8) semiconducting glasses

Results of phase transformations, enthalpy released and specific heat of Ge22Se78−xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, Tg, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of Tg (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of Tg, at a heating rate of 5 K min−1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol−1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference Tc−Tg and the enthalpy released during the crystallization process. Below Tg, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.

Differential scanning calorimetry studies of Se85Te15−x Pb x (x = 4, 6, 8 and 10) glasses

Results of differential scanning calorimetry (DSC) studies of Se85Te15−xPbx (x = 4, 6, 8 and 10) glasses have been reported and discussed in this paper. The results have been analyzed on the basis of structural relaxation equation, Matusita’s equation and modified Kissinger’s equation. The activation energies of structural relaxation lie in between 226 and 593 kJ/mol. The crystallization growth is found to be onedimensional for all compositions. The activation energies of crystallization are found to be 100–136 kJ/mol by Matusita’s equation while 102–139 kJ/mol by modified Kissinger’s equation. The Hruby number (indicator of ease of glass forming and higher stability) is the highest for Se85Te9Pb6 glass while S factor (indicator of resistance to devitrification) is highest for Se85Te7Pb8 glass at all heating rates in our experiment. Further the highest resistance to devitrification has the highest value of structural activation energy and the activation energy of crystallization is maximum for the most stable glass by both Matusita’s equation and the modified Kissinger’s equation.

Crystallization kinetics and optical band gap studies of Se96In4 glass before and after slow neutron irradiation

Abstract Results of differential scanning calorimetry (DSC) under non-isothermal condition on Se 96 In 4 semiconducting chalcogenide glass before and after slow neutron irradiation, for different exposure times, have been reported and discussed. Some of Sn atoms have been injected into the glass by nuclear transmutation processes and the binary glass is converted into a ternary. This is accompanied by an increase in the activation energy of crystallization, E c , and in the glass transition temperature, T g and a decrease in the glass transition activation energy, E t , in the onset crystallization temperature, T c and in the peak temperature of crystallization T p . Optical band gap measurements have also been carried out, before and after irradiation, on identical thin pellets of Se 96 In 4 glass. The energy band gap, E g , is found to decrease upon irradiation. These effects have been attributed to a structural change upon doping and to irradiation induced defects.

Simultaneous measurements of thermal conductivity and diffusivity of Se80Te20-xInx (x = 2, 4, 6 and 10) chalcogenide glasses at room temperature

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se80Te20-xInx (x = 2, 4, 6 and 10) glasses, prepared under a load of 5 tons were carried out at room temperature using transient plane source (TPS) technique. The measured values of both thermal conductivity and diffusivity were used to determine the specific heat per unit volume of the said materials in the composition range of investigation. Results indicated that both the values of thermal conductivity and thermal diffusivity increased with the addition of indium at the cost of tellurium whereas the specific heat remained almost constant. This compositional dependence behaviour of the thermal conductivity and diffusivity has been explained in terms of the iono-covalent type of bond which In makes with Se as it is incorporated in the Se-Te glass.

Phase transformations of binary Se100−xInx (x=2, 4 and 10) semiconducting chalcogenide glasses under isothermal condition

Solid state phase transformations are encountered in many processes and are of great practical importance; therefore, they continue to be intensively studied. Since thermo-analytical techniques are simple and informative, they are increasingly being employed to investigate these transformations. Basically there are two different conditions, namely isothermal and nonisothermal, under which the crystallization kinetics can be studied. Successful application of the thermoanalytical results to an understanding of the processes involved in transformations requires suitable methods for analyzing the experimental data. The analysis of the data obtained has been carried out using different theoretical approaches [1–7], which have been formulated based on the formal theory of transformation kinetics. Selenium based binary chalcogenide glasses are found to be more useful in practical applications than pure selenium [8, 9]. From a technological point of view, these glasses should be thermally stable with time and temperature during use. In the non-isothermal method the stability against crystallization is often reported in terms of the temperature interval between the glass transition temperature, Tg, and the onset temperature for crystallization, Tc, detected during heating of a preformed sample at a steady rate. In case of isothermal technique, the stability against crystallization cannot be determined in terms of temperature difference ( Tg and Tc are not relevant). Therefore, an attempt has been made to ensure the stability through the calculation of the number of nucleation sites. Moreover, Tg and Tc even in non-isothermal condition cannot be determined precisely due to the fact that the kinetics of phase transformations depends on a variety of parameters [10]. The aim of the present letter is to report the effect of indium impurity on the stability of amorphous selenium and to study the transformation kinetics of the resulting binary Se-In under isothermal condition using differential scanning calorimetry (DSC). High purity (99.999%) selenium and indium in the appropriate atomic percentages were weighed into quartz ampoules (length 5 cm and internal diameter 8 mm). The contents of the ampoule (5 gm) were sealed in a vacuum of 10 −6 Torr and heated in a furnace where the temperature was raised at a rate of 3–4 K per minute up to 925 K and kept around that temperature for 7–8 h to ensure the homogeneity of the samples. The molten samples were then rapidly quenched in ice cooled water. The glassy nature of the alloys was ascertained by XRD. A Perkin-Elmer differential scanning calorimeter (DSC-2) was used for isothermal studies of the samples. The samples were introduced into the DSC cell and heated to a temperature 50 K below the target temperature, and after holding it at this temperature for 40 s, they were taken to the target temperature at a high heating rate of 20 K/min. Isothermal curves were recorded at four different annealing temperatures for each sample of the Se100−xInx (x= 2, 4 and 10) chalcogenide glasses. Since the data of first 40 s were lost while the instrument was being stabilized; a correction was made by simply taking the origin at t = 40 s and assuming that no crystallization had taken place before t = 40 s at the properly chosen isothermal temperature. Fig. 1 shows isothermal DSC thermogram of binary Se 98In2 glass at 381.1 K, as an example. For the sake of accuracy four measurements were conducted for each isothermal temperature while keeping each specimen under identical conditions. The theoretical description of the progress of the solid state transformation has been developed by considering the geometrical problem of impingement of growing fronts. This led to the derivation of a relationship called the Johnson-Mehl-Avrami (JMA) Equation [4–7]. According to this equation the value, X of the