Deepika Bhandari

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 Se85—xTe15Sbx Glasses with x = 0, 2, 4, 6, 8 and 10

Results of Differential Scanning Calorimetry (DSC) under non-isothermal condition of Se 85-x Te 15 Sb x (x = 0, 2, 4, 6, 8 and 10) glasses are reported and discussed. The glass transition temperature at different heating rates and structural changes during glass transition have been determined from an empirical relation. The activation energies for crystallization have been determined from the heating rate dependence of the peak crystallization temperatures. The results have been analyzed using Kissingers and Matusitas equations and the modified Ozawa equation for non-isothermal crystallization of materials. The variation of the glass transition temperature with composition suggests that a small amount of Sb(4 at%) leads to an increase in the chain length of Se-Te, whereas further increase in the Sb atomic percentage increases the number of Se-Te chains in the alloys. The thermal stability (T c - T g ) is found to be maximum at 4 at% Sb and suggests that this alloy can be considered as a critical composition at which the system becomes chemically ordered. Moreover, the minimum heat released during crystallization at this composition confirms the maximum stability of the alloy.

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 of CuxTi100-x (x = 43, 50 and 53) glasses

Abstract The crystallization kinetics of Cu–Ti glass at three different compositions has been studied by differential scanning calorimetry (DSC). The DSC traces have been analyzed in terms of activation energy, stability and dimensionality of growth by four different models viz. the Kissinger equation, the Ozawa equation, the Matusita equation and the Gao and Wang equation. The activation energy increases with Cu content and the highest crystallization temperature occurs for the composition Cu50Ti50 indicating locally increased chemical short-range order at this particular composition. The average value of the Avrami exponent comes out to be 4 which shows that the crystallization process takes place via three-dimensional parabolic growth with bulk crystallization.

Structure and dynamics of a two-component metallic glass

Computations of the frequencies of longitudinal and transverse phonon modes in a two-component metallic glass (Mg70Zn30) based on the pseudopotential approach used for the calculation of interatomic pair potential have been presented. The theory employed for these calculations is a self-consistent phonon theory as developed by Takeno and Goda (1971) for amorphous solids. The computed results are compared with molecular dynamics and neutron inelastic scattering experiments. It appears that the short-wavelength collective excitations detected in this glass arise from longitudinal phonon excitations and probably not from a diffuse Umklapp scattering from transverse acoustic waves.

Effect of high-energy heavy ion irradiation on the crystallization kinetics of Co-based metallic glasses

Differential scanning calorimeter (DSC) is employed to study the crystallization kinetics of irradiated (at three different fluences with high-energy heavy ion; Ni11+ of 150 MeV) specimens of two Co-based metallic glasses. It is found that the crystallization process in both the glasses is completed in two phases. The DSC data have been analysed in terms of kinetic parameters viz. activation energy (Ec), Avrami exponent (n), dimensionality of growth (m), bdusing two different theoretical models. The results obtained have been compared with that of virgin samples. The lower activation energy in case of second crystallization occurring at higher temperature indicates the easier nucleation of second phase. The abnormally high value of Avrami exponent in Co-Ni glass indicates very high nucleation rate during first crystallization.

Structure and vibrational dynamics of Ca70Mg30 glass

Abstract A new effective pair potential is proposed for Ca 70 Mg 30 glass in Ashcroft form using the concept of a Wigner-Seitz sphere treating it as a one-component system. A theory of phonon in amorphous solids in a generalized random phase approximation is employed to compute the eigenfrequencies of the longitudinal and transverse phonons making use of the so obtained potential. The eigenfrequencies obtained agree qualitatively with the neutron inelastic scattering results of Suck et al . and also with the theoretical results of Hafner and with the results of Bhatia and Singh, both qualitatively as well as quantitatively. In addition, the elastic and thermodynamic properties of the glass have also been studied using the longitudinal and transverse sound velocities.