Browsing by Author "N. Mehta"

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A brief review of amorphous semiconductors
(Elsevier Ltd, 2023) Shobhit Saraswat; V.K. Tomar; V.K. Deolia; N. Mehta
One ongoing major problem in solid-state physics is to understand the effect of disorder on the properties of materials. Disordered materials often display novel properties as compared to their crystalline counterpart. Many of these properties are useful for various technological applications, such as window glass, solar cells, etc. Disordered or amorphous materials are desirable for application because they are cheaper to manufacture and, therefore, their study is highly significant and it establishes the necessities of academic and industrial applications. It is also very challenging since many of these existing experimental techniques and theoretical formalisms which have been developed for crystals are either inapplicable or require modification. The present paper reports an overview the amorphous semiconductors. The paper starts with the historical growth of amorphous semiconductors and covers all basic perspectives of Chalcogenide glasses (ChGs) that are a renowned example of amorphous semiconductors. © 2023
A new approach for nano-structuring of glassy selenium (g-Se) using silver nanoparticles (AgNPs) as precursor
(Elsevier Ltd, 2021) Amit Kumar; N. Mehta; A. Dahshan
Various routes have been proposed for the synthesis of chalcogen based nanostructured materials but the search of conventional and cost-effective method for the nanostructuring of chalcogenides is an ongoing research activity. This unique work reports the synthesis and the characterization of a novel kind of glassy nanocomposite material belonging to the nano-structuring of g-Se with the help of silver nanoparticles. The local structure is analyzed with the help of X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, and Differential Scanning Calorimetry. It was found that the addition of AgNPs in glassy Se creates fine nano-wires of trigonal Selenium (t-Se) in the glass matrix of g-Se. The electrical, mechanical, and thermal characterizations of the present glassy nanocomposite material have been done in terms of current-voltage characteristics, d.c. conductivity, micro-hardness, and kinetic parameters of glass/crystal phase transformation. A comparative analysis of present glassy composites with a conventional Ag containing glassy alloy (g-Se98Ag2) has also been done to understand the role of incorporation of silver nanoparticles over the normal silver powder. The detailed analysis shows that different physical properties [e.g., thermal stability, modulus of elasticity, micro-hardness, the threshold voltage (i.e., turn-on voltage for resistive switching), and d.c. conductivity] are enhanced more effectively when the nano-structuring of g-Se by using AgNPs is executed as compared to the routine way of alloying. © 2020 Elsevier Ltd
A study of some thermophysical parameters in glassy Se80Te 20 and Se80Te10M10 (Cd, In, and Sb) alloys
(2013) N. Chandel; N. Mehta
The present paper reports a comparative study of some thermophysical properties (thermal conductivity, thermal diffusivity, thermal effusivity, and specific heat per unit volume) for Se80Te20 and Se 80Te10M10 (Cd, In, and Sb) alloys. The transient plane source technique is used for this purpose. The thermal conductivity is highest for Se80 Te10 In10 as compared to the other ternary alloys. This is explained in terms of the thermal conductivity of additive elements Cd, In, and Sb. The composition dependence of the thermal diffusivity and specific heat per unit volume is also discussed. © 2013 Springer Science+Business Media New York.
Amorphous to crystalline phase transition in glassy Se65Te20Ag15 alloy
(2009) R.S. Tiwari; D. Kumar; N. Mehta
In the present work, the amorphous to crystalline phase transition of chalcogenide glass Se65Te20Ag15 has been studied using differential scanning calorimetric (DSC) measurements. The heating rate dependence of crystallization peaks has been used for the determination of activation energies of glass transition (Eg) and crystallization (Ec). Different non-isothermal methods have been used for this purpose. Other useful kinetic parameters such as the order parameter (n), the numerical factor of crystallization mechanism (m) and the frequency factor (Ko) of the rate constant (K) have been also determined.
Analysis of composition dependence of some thermal transport properties in glassy Se80-xTe20Snx (0 ≤ x ≤ 10) alloys using transient plane source measurements
(Elsevier B.V., 2013) A. Sharma; N. Mehta
In the present work, we have studied simultaneous measurements of thermal transport properties (effective thermal conductivity, diffusivity, specific heat per unit volume, thermal inertia IT) of glassy Se80- xTe20Snx (0 ≤ x ≤ 10) system using their twin pellets. The glassy system is prepared under a load of 5 tons and measurements have been made at room temperature using Transient Plane Source (TPS) technique. The composition dependence of the thermal transport properties of given glassy system is also discussed. © 2012 Elsevier Ltd. All rights reserved.
Analysis of dielectric relaxation in glassy Se and Se 98M 2 (M = Ag, Cd and Sn) alloys: A study of metal-induced effects
(2012) A. Sharma; N. Mehta
The present work reports the temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε′′) in binary Se 98M 2 (Ag, Cd and Sn) alloys. The measurements have been made in the frequency range (1-500 kHz) and in the temperature range 297-345 K. The values of dielectric constant (ε′) and dielectric loss (ε′′) were found to decrease with frequency and increase with temperature. The maximum barrier height W m is calculated from dielectric measurements according to the Guintini equation. The results indicate that the dielectric dispersion exists in the present glassy systems in the above frequency and temperature range. © EDP Sciences, 2012.
Calorimetric studies of non-isothermal crystallization in amorphous Cu xTi100-x alloys
(2011) N. Mehta; K. Singh; N.S. Saxena
The present paper reports the composition dependence of pre-exponential factor and activation energy of non-isothermal crystallization in amorphous alloys of CuxTi100-x system using differential scanning calorimeter (DSC) technique. The applicability of Meyer-Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization for amorphous alloys of Cu-Ti system was verified. © Indian Academy of Sciences.
Calorimetric studies of thermal crystallization in glassy Se 80-xTe20Snx (0≤x≤10) alloys
(2011) H. Kumar; N. Mehta; K. Singh
This paper reports a calorimetric study of the crystallization kinetics in glassy Se80-xTe20Snx (0≤x≤10) alloys in terms of kinetic parameters of crystallization (crystallization temperature Tc, activation energy of crystallization Ec and order parameter n) and thermodynamic parameters of crystallization (enthalpy of crystallization Hc and the entropy of crystallization Sc). © 2011 The Royal Swedish Academy of Sciences.
Calorimetric study of specific heat in glassy Se-Te-Sn-Bi system using MDSC technique: Effect of Bi incorporation
(2013) A. Sharma; H. Kumar; N. Mehta
Bismuth has historical significance as a modifier in chalcogenide glasses due to the p- to n-type transition at a particular composition of definite glassy systems after its incorporation. We have synthesized some new quaternary glasses using Bi as a modifier in ternary Se78Te20Sn 2 alloy as parent glass in light of this information. Modulated differential scanning calorimetry measurements have been made on glassy Se 78-x Te20Sn2Bix (0 ≤ x ≤ 6) alloys for specific heat studies. We have observed an expected enormously large increase in the specific heat values in the glass transition region. The composition dependence of specific heat values above the glass transition temperature (Cpe) and below the glass transition (Cpg) is also discussed in this article. © 2013 Copyright Taylor and Francis Group, LLC.
Calorimetric study of thermal crystallization kinetics in Se78−xTe20Sn2Pbx (0 ≤ x ≤ 6) alloys
(2013) H. Kumar; N. Mehta
Glassy samples of Se78−xTe20Sn2Pbx (0 ≤ x ≤ 6) system are prepared by melt quenching method. For non-isothermal study of crystallization kinetics, DSC scans have been taken at the heating rates 5, 10, 15 and 20 K/min in non-isothermal mode. Activation energy of crystallization (Ec) has been calculated using Kissinger method, Matusita-Sakka method and Augis-Bennett method. Various kinetic parameters of crystallization kinetics like peak crystallization temperature (Tc), Rate constants (K) and order parameter (n) are determined using these DSC scans. Thermodynamic parameters such as crystallization enthalpy (ΔHc) and entropy change during the crystallization (ΔS) are also evaluated. Results are discussed using chemical bond approach. © EDP Sciences 2013.
Chemical bond approach to optical band gap in Se100-xSb x chalcogenide glasses
(National Institute of Optoelectronics, 2011) S. Srivastava; N. Mehta; R.S. Tiwari; R.K. Shukla; A. Kumar
In the present work, values of the optical band gap Eg of glassy Se 100-xSbx alloys are determined from experimentally observed data of transmission at different wavelengths using three different methods. The theoretical prediction of Eg values is also made using random bond network model proposed by Shimakawa.The composition dependence of Eg is discussed using chemical bond approach.
Co-relation between pre-exponential factor and activation energy of non-isothermal crystallization for virgin and irradiated Fe78B13Si9 metallic glass
(2009) N. Mehta; K. Singh; N.S. Saxena
The present work shows the applicability of Meyer-Neldel relation between the pre-exponential factor and activation energy of non-isothermal crystallization of Fe78B13Si9 metallic glass. Differential scanning calorimeter (DSC) technique is used to observe the variation in the above two kinetic parameters of the non-isothermal crystallization due to ionic irradiation at three different fluences with high-energy heavy ion Ni11+ having energy 150 MeV. © 2009 Elsevier B.V. All rights reserved.
Comparative analysis of some thermo-physical properties of Se90Zn10 and Te90Zn10 alloys
(2008) N. Mehta; K. Singh; N.S. Saxena
The present paper reports a comparative study of some thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of Se90Zn10 and Te90Zn10 alloys. Simultaneous measurements of effective thermal conductivity (λe) and effective thermal diffusivity (χe) of twin pellets of Se90Zn10 and Te90Zn10 alloys using transient plane source (TPS) technique have been made at room temperature. From the measured values of λe and χe, the specific heat per unit volume (Cv) has been calculated. The results indicate that the measured values of these parameters are higher for Te90Zn10 alloy as compared to Se90Zn10 alloy. This is explained in terms of thermal conductivity of chalcogen elements Se and Te. © 2008 Elsevier B.V. All rights reserved.
Comparative analysis of thermal crystallization in Cu50Ti50 and Cu50Zr50 metallic glasses
(2008) N. Mehta; K. Singh; N.S. Saxena
The present paper reports a comparative study of crystallization kinetics in two important metallic glasses Cu50Ti50 and Cu50Zr50 in terms of kinetic parameters of crystallization (activation energy of crystallization Ec, crystallization temperature Tc and rate of crystallization K) and thermodynamic parameter of crystallization (enthalpy of crystallization Hc and the specific heat Cp of crystallization). The results are explained in terms of physical properties of additive elements M=Ti and Zr in Cu50M50 system. © 2008 Elsevier B.V. All rights reserved.
Composition dependence of some thermo-physical properties of multi-component Se78−xTe20Sn2Bi x (0 ≤ x ≤ 6) chalcogenide glasses
(Springer New York LLC, 2015) A. Sharma; N. Mehta
New multi-component glassy materials with composition of Se78−xTe20Sn2Bix (0 ≤ x ≤ 6) have been synthesized by well-known melt quenching technique. The as-prepared glasses have been characterized by applying an advanced transient plane source technique to study their thermal transport properties (effective thermal conductivity, diffusivity, specific heat per unit volume) at room temperature. Density measurements have been done to correlate the obtained results. Using the experimental data of density measurements, the basic physical parameters, such as mean atomic volume, compactness, average coordination number etc., are evaluated for the synthesized glasses and the results are discussed as a function of glass composition. We have also determined the phonon mean free path (τ) using the experimental value of effective thermal diffusivity. The composition dependence of the thermal transport properties of aforesaid glassy system has also been discussed. © 2014, Springer Science+Business Media New York.
Composition dependence of specific heat in Se80-x Te 20Sn x chalcogenide glasses
(2013) A. Sharma; H. Kumar; N. Mehta
Differential Scanning Calorimetry (DSC) is performed at different heating rates under non-isothermal conditions to study the specific heat studies of glassy Se80 - x Te20Sn x (0 ≤ x ≤ 10) alloys. An extremely large increase in the specific heat values has been observed at the glass transition temperature. It has also been found that the values of C p below glass transition temperature (C pg ) and after glass transition (C pe ) are highly composition dependent. This indicates that the Sn additive used in the present study influences the structure of the glassy Se80Te20 alloy. The results show that C p values reveal local extrema in Se-Te-Sn glassy system at x = 4 and x = 8. The composition dependence of both parameters (C pe and C pg ) has been explained in terms of the glassy structure of Se-Te-Sn system. © 2013 Pleiades Publishing, Ltd.
Composition dependence of the activation energy of the glass transition in some chalcogenide glasses
(2008) N. Mehta; A. Kumar
The activation energy (Et) of the glass transition process has been obtained for glassy Se80-xTe20Mx (M = Ag, Cd, In, Sb) and Se100-xMx (M = In, Te, Sb) systems using differential scanning calorimetry. The composition dependence of Et is explained in terms of fragility index for the systems. A reversal in the trend of the Et is explained using topological models.
Composition dependence of thermal stability, micro-hardness and compactness in glassy Se90In10-xGex alloys
(2009) H. Kumar; N. Mehta; K. Singh; A. Kumar
In the present work, the effect of Ge incorporation is studied on the thermal stability, micro-hardness and compactness of glassy Se90In10 alloy. Thermal stability of glassy Se90In10-xGex alloys has been studied using differential scanning calorimetric technique. Micro-hardness of glassy Se90In10-xGex alloys is measured at room temperature. The compactness of the structure of Se90In10-xGex alloys is also determined from the measured densities. The variation in micro-hardness and compactness with composition has been discussed. © 2009 Elsevier B.V. All rights reserved.
Critical analysis of endo-thermal effect in the glass transition process in chalcogenide glasses
(2012) N. Mehta; A. Kumar
Free volume model is widely used as a tool for understanding the nature of glass transition phenomenon and the related consequences. Recently, an analytical derivation of Kissinger's equation has been proposed in literature using free volume model. In this derivation, the glass transition activation energy has been assumed constant throughout the whole glass transition temperature range. The present paper investigates the applicability of free volume model for derivation of Kissinger's relation by checking the constancy of the glass transition activation energy (E g) throughout the glass transition temperature range. Performing series of experiments, we have legalized the possibility for usage of the Kissinger relation for determination of the glass transition activation energy if the peak value of the endo-thermal effect is taken as temperature of glass transition. © 2012 Elsevier B.V.
Crystallization kinetics and Avrami index of Sb-doped Se–Te–Sn chalcogenide glasses
(Taylor and Francis Ltd., 2018) D.K. Dwivedi; Vandita Rao; N. Mehta; N. Chandel
Bulk amorphous samples of Sb-substituted Se78 − xTe20Sn2Sbx (0 < x < 6) have been prepared using melt quench technique. The structure of Se78− xTe20Sn2Sbx (x = 0, 2, 4, 6) glassy alloys has been investigated using X-ray diffraction technique. Calorimetric studies of the prepared samples have been performed under non-isothermal conditions using differential scanning calorimetry (DSC) and glass transition temperature as well as crystallization temperature has been evaluated using DSC scans. The activation energy of crystallization kinetics (Ec) has been determined using model-free approaches such as Kissinger, Ozawa, Tang and Starink methods. The Avrami index (n) and frequency factor (Ko) have been calculated by Matusita and Augis–Benett method. © 2018 Informa UK Limited, trading as Taylor & Francis Group.