The crystallization of metallic glasses has been studied quite extensively using differential sca... more The crystallization of metallic glasses has been studied quite extensively using differential scanning calorimetry (DSC) technique. Most methods rely on isokinetic hypothesis for the kinetic analysis of crystallization for which the choice of a reliable model is very important. Due to inherent uncertainty in the determination of kinetic parameters, the model-free isoconversional analytical techniques were proposed. However, these isoconversional methods are scarcely used for metallic glasses. In the present work, the crystallization kinetics of Fe67Co18B14Si1 metallic glass through both isoconversional and isokinetic methods has been investigated and attention has been focused on the relative applicability of the two methods.
Capacitors are the most convenient and economical devices for storage of electrical energy. Perfo... more Capacitors are the most convenient and economical devices for storage of electrical energy. Performance of a capacitor is primarily governed by solid-state characteristics of its dielectric material and the explicit value of the dielectric constant. Titanate ceramics such as Barium Titanate are popular capacitor dielectric materials because of their high dielectric constant and ferroelectric properties. In recent years, extensive research
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
In this study, an effort has been made to synthesize nano-scale barium titanate powder by sol-gel... more In this study, an effort has been made to synthesize nano-scale barium titanate powder by sol-gel and hydrothermal methods. Characterization of the synthesized Barium Titanate is conducted by using X-ray diffraction for crystallite size, Transmission Electron Microscopy for particle size and scanning electron microscopy for surface morphology. It is observed that the powders prepared by Sol-gel and hydrothermal routes have
Kinetics of crystallization process in a Fe-based metallic glass 2826A (FeââNiââCrââPââBâ) has ... more Kinetics of crystallization process in a Fe-based metallic glass 2826A (FeââNiââCrââPââBâ) has been studied with the help of differential scanning calorimetry(DSC). It is found that the 2826A metallic glass exhibits two overlapping crystallization peaks. The activation energy for crystallization (E) and the Avrami exponent (n) for the two crystallization peaks have been obtained using the Kolmogorov-Jhonson-Mehl-Avrami (KJMA) equation. The so-obtained values of E and n have been utilized to derive normalized heat flow curves. It has been observed that the theoretical heat flow curves obtained using KJMA equation show large deviations from the experimental curves for the first peak whereas the curves are in very close agreement for the second peak. This suggests that kinetics of crystallization process during the first peak cannot be described correctly in KJMA formalism.
Studies on nanocrystalline materials require an accurate determination of crystallite size as wel... more Studies on nanocrystalline materials require an accurate determination of crystallite size as well as the microstrains induced in the material. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the two well-known techniques for this purpose. Based on XRD ...
Progress in Crystal Growth and Characterization of Materials
Cu-Zr is among the family of the binary metallic glasses which are well-known for their superior ... more Cu-Zr is among the family of the binary metallic glasses which are well-known for their superior mechanical and magnetic properties. From the structure point of view, the amorphous metallic glasses are in non-equilibrium solid state. Therefore, it becomes important to study the factors, which may have crucial bearings on its end applications, related to the amorphous metallic structures. Stability is an important factor related to crystallization, which is generally a thermally activated process of transition from a disordered amorphous structure to an ordered crystal structure. Study of kinetics of crystallization provides Ec, the activation energy of crystallization and parameters like Avrami exponent n, responsible for the mechanism of crystallization. This helps to determine the thermal stability of the metallic glasses.Cu50Zr50 metallic glass had been prepared by single roller melt-spinning technique. The DSC thermogram recorded at four different heating rates exhibits a two st...
The phonon spectra for liquid Li and Na have been computed through the phenomenological model of ... more The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li0.61Na0.39 alloy...
ABSTRACT Structural relaxation of isothermally and iscochronally heat treated Ge1-xSnxSe2.5 (x = ... more ABSTRACT Structural relaxation of isothermally and iscochronally heat treated Ge1-xSnxSe2.5 (x = 0.3, 0.5) glassy alloys have been studied using a differential scanning calorimeter under non-isothermal conditions. Relaxation enthalpies in the vicinity of glass transition have been recorded on the basis of heat capacity curves of annealed and unannealed samples. Besides relaxation enthalpy, activation energy of structural relaxation for both annealed and unannealed samples have been determined using Kissinger formalism. The results predict that sub-Tg annealing of glass leads to decrease in enthalpy of system thereby taking it to more equilibrium configuration. It is also observed that activation energy of structural relaxation is lower for annealed sample than unannealed sample and therefore glass transition occurs at a lower temperature.
The present paper reports the investigations on structural relaxation of Se58Ge42-xPbx (9<=x&l... more The present paper reports the investigations on structural relaxation of Se58Ge42-xPbx (9<=x<=20) glasses through the study of phase transformation and thermodynamics carried out using differential scanning calorimetry (DSC). The DSC thermograms at constant heating rates exhibit single glass transition and double crystallization on heating, indicating the occurrence of phase separation in these glasses. It has been found through the X-ray diffraction (XRD) that glasses get crystallized into GeSe2 and PbSe/Se phases after annealing for 2 hrs at an intermediate temperature between first and second crystallization. Kinetics of phase transformation of these glasses studied earliar through the kinetic parameters like activation energy of glass transition and crystallization, avrami exponent, dimensionality of growth show that increase in lead (Pb) contents increases the thermal stability of the glassy samples. The thermodynamic study made through the determination of parameters like specific heat, entropy difference between metastable states as well as glass and crystalline state, Gibbs free energy difference between glass and crystalline state and enthalpy released during phase transformation (glassy to crystalline) reveals that Se58Ge22Pb20 glass has highest thermal stability among the other samples if the series. An effort has also been made to study the structural relaxation in the vicinity of glass transition in these glasses. The structural relaxation of Se58Ge42-xPbx (x = 9, 18) glassy samples has been studied in terms of excess specific heat and excess enthalpy in the glass transition region. Excess specific heat has been obtained using the specific heat of the as-prepared sample and that obtained by annealing the sample at two different temperatures below glass transition temperature. The values of excess enthalpy show that Se58Ge24Pb18 glass is more stable than Se58Ge33Pb9 glass, a conclusion which has already been drawn from the study of kinetics of phase transformations and thermodynamics.
The crystallization of metallic glasses has been studied quite extensively using differential sca... more The crystallization of metallic glasses has been studied quite extensively using differential scanning calorimetry (DSC) technique. Most methods rely on isokinetic hypothesis for the kinetic analysis of crystallization for which the choice of a reliable model is very important. Due to inherent uncertainty in the determination of kinetic parameters, the model-free isoconversional analytical techniques were proposed. However, these isoconversional methods are scarcely used for metallic glasses. In the present work, the crystallization kinetics of Fe67Co18B14Si1 metallic glass through both isoconversional and isokinetic methods has been investigated and attention has been focused on the relative applicability of the two methods.
Capacitors are the most convenient and economical devices for storage of electrical energy. Perfo... more Capacitors are the most convenient and economical devices for storage of electrical energy. Performance of a capacitor is primarily governed by solid-state characteristics of its dielectric material and the explicit value of the dielectric constant. Titanate ceramics such as Barium Titanate are popular capacitor dielectric materials because of their high dielectric constant and ferroelectric properties. In recent years, extensive research
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
In this study, an effort has been made to synthesize nano-scale barium titanate powder by sol-gel... more In this study, an effort has been made to synthesize nano-scale barium titanate powder by sol-gel and hydrothermal methods. Characterization of the synthesized Barium Titanate is conducted by using X-ray diffraction for crystallite size, Transmission Electron Microscopy for particle size and scanning electron microscopy for surface morphology. It is observed that the powders prepared by Sol-gel and hydrothermal routes have
Kinetics of crystallization process in a Fe-based metallic glass 2826A (FeââNiââCrââPââBâ) has ... more Kinetics of crystallization process in a Fe-based metallic glass 2826A (FeââNiââCrââPââBâ) has been studied with the help of differential scanning calorimetry(DSC). It is found that the 2826A metallic glass exhibits two overlapping crystallization peaks. The activation energy for crystallization (E) and the Avrami exponent (n) for the two crystallization peaks have been obtained using the Kolmogorov-Jhonson-Mehl-Avrami (KJMA) equation. The so-obtained values of E and n have been utilized to derive normalized heat flow curves. It has been observed that the theoretical heat flow curves obtained using KJMA equation show large deviations from the experimental curves for the first peak whereas the curves are in very close agreement for the second peak. This suggests that kinetics of crystallization process during the first peak cannot be described correctly in KJMA formalism.
Studies on nanocrystalline materials require an accurate determination of crystallite size as wel... more Studies on nanocrystalline materials require an accurate determination of crystallite size as well as the microstrains induced in the material. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are the two well-known techniques for this purpose. Based on XRD ...
Progress in Crystal Growth and Characterization of Materials
Cu-Zr is among the family of the binary metallic glasses which are well-known for their superior ... more Cu-Zr is among the family of the binary metallic glasses which are well-known for their superior mechanical and magnetic properties. From the structure point of view, the amorphous metallic glasses are in non-equilibrium solid state. Therefore, it becomes important to study the factors, which may have crucial bearings on its end applications, related to the amorphous metallic structures. Stability is an important factor related to crystallization, which is generally a thermally activated process of transition from a disordered amorphous structure to an ordered crystal structure. Study of kinetics of crystallization provides Ec, the activation energy of crystallization and parameters like Avrami exponent n, responsible for the mechanism of crystallization. This helps to determine the thermal stability of the metallic glasses.Cu50Zr50 metallic glass had been prepared by single roller melt-spinning technique. The DSC thermogram recorded at four different heating rates exhibits a two st...
The phonon spectra for liquid Li and Na have been computed through the phenomenological model of ... more The phonon spectra for liquid Li and Na have been computed through the phenomenological model of Bhatia and Singh for disordered systems like liquids and glasses and the obtained results have been compared with the available data obtained by inelastic neutron scattering (INS) and inelastic X-ray scattering (IXS) experiments. The effective pair potentials and their space derivatives are important ingredients in the computation of the dispersion curves. The pair potentials are obtained using the pseudo-potential theory. The empty core model proposed by Ashcroft is widely used for pseudo-potential calculations for alkali metals. But, it is thought to be unsuitable for Li because of its simple 1s electronic structure. However, it can be used with an additional term known as Born-Mayer (BM) core term. The influence of the BM core term on the phonon dispersion is discussed. The same pseudo-potential formalism has been employed to obtain the dispersion relation in liquid Li0.61Na0.39 alloy...
ABSTRACT Structural relaxation of isothermally and iscochronally heat treated Ge1-xSnxSe2.5 (x = ... more ABSTRACT Structural relaxation of isothermally and iscochronally heat treated Ge1-xSnxSe2.5 (x = 0.3, 0.5) glassy alloys have been studied using a differential scanning calorimeter under non-isothermal conditions. Relaxation enthalpies in the vicinity of glass transition have been recorded on the basis of heat capacity curves of annealed and unannealed samples. Besides relaxation enthalpy, activation energy of structural relaxation for both annealed and unannealed samples have been determined using Kissinger formalism. The results predict that sub-Tg annealing of glass leads to decrease in enthalpy of system thereby taking it to more equilibrium configuration. It is also observed that activation energy of structural relaxation is lower for annealed sample than unannealed sample and therefore glass transition occurs at a lower temperature.
The present paper reports the investigations on structural relaxation of Se58Ge42-xPbx (9<=x&l... more The present paper reports the investigations on structural relaxation of Se58Ge42-xPbx (9<=x<=20) glasses through the study of phase transformation and thermodynamics carried out using differential scanning calorimetry (DSC). The DSC thermograms at constant heating rates exhibit single glass transition and double crystallization on heating, indicating the occurrence of phase separation in these glasses. It has been found through the X-ray diffraction (XRD) that glasses get crystallized into GeSe2 and PbSe/Se phases after annealing for 2 hrs at an intermediate temperature between first and second crystallization. Kinetics of phase transformation of these glasses studied earliar through the kinetic parameters like activation energy of glass transition and crystallization, avrami exponent, dimensionality of growth show that increase in lead (Pb) contents increases the thermal stability of the glassy samples. The thermodynamic study made through the determination of parameters like specific heat, entropy difference between metastable states as well as glass and crystalline state, Gibbs free energy difference between glass and crystalline state and enthalpy released during phase transformation (glassy to crystalline) reveals that Se58Ge22Pb20 glass has highest thermal stability among the other samples if the series. An effort has also been made to study the structural relaxation in the vicinity of glass transition in these glasses. The structural relaxation of Se58Ge42-xPbx (x = 9, 18) glassy samples has been studied in terms of excess specific heat and excess enthalpy in the glass transition region. Excess specific heat has been obtained using the specific heat of the as-prepared sample and that obtained by annealing the sample at two different temperatures below glass transition temperature. The values of excess enthalpy show that Se58Ge24Pb18 glass is more stable than Se58Ge33Pb9 glass, a conclusion which has already been drawn from the study of kinetics of phase transformations and thermodynamics.
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