Browsing by Author "N. Chandel"

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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.
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.
Effect of antimony on glass transition and thermal stability of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6 at.%) multicomponent glassy alloys
(Springer Netherlands, 2018) Vandita Rao; N. Chandel; N. Mehta; D.K. Dwivedi
Multicomponent glassy alloys Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6) have been synthesized using melt quench technique. The prepared samples have been characterized by X-ray diffraction technique and differential scanning calorimetry (DSC). Glass transition kinetics of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6 at.%) glassy alloys has been examined using DSC. DSC runs have been recorded at different heating rates (5, 10, 15 and 20 K min−1) for each sample under investigation. Heating rate dependence of glass transition temperature (Tg) has been studied using Lasocka empirical relation. The activation energy of glass transition has been evaluated using Kissinger and Moynihan’s relation. The effect of antimony concentration on glass transition temperature and activation energy has been investigated in the prepared samples. Glass-forming ability and thermal stability of Se78−xTe18Sn2Sbx (x = 0, 2, 4 and 6) glassy alloys have been monitored through the evaluation of thermal stability using Dietzal relation, Hurby parameter, and Saad and Poulin parameter. The above-mentioned parameters are found to be compositionally dependent, which indicates that among the studied glass samples the stability is maximum for Sb at 2% content. © 2018, Akadémiai Kiadó, Budapest, Hungary.
Effect of laser-irradiation on some significant physical properties of SeTeIn glass-ceramic
(Institute of Physics, 2023) N. Chandel; H.I. Elsaeedy; N. Mehta
Laser irradiation on the samples of electronic/optical materials is a versatile tool to modify the structural morphology without changing their composition. We have explored the micro-structural changes (e.g., crystal size, defect state density, etc) induced by the He-Ne laser in Se80Te10In10 alloy. A systematic and detailed investigation of the laser-induced effects in Se80Te10In10 alloy has been undertaken using combinations of microscopic and macroscopic probe techniques like Differential Scanning Calorimeter (DSC), x-ray diffractometer (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM). Investigations of the structural, thermal, electrical, and spectroscopic characterization of the Se80Te10In10 alloy have been compared before and after laser exposure. The glass transition/crystallization enthalpies and dielectric constant/loss are significantly increased after laser exposure. The results of structural characterization show that exposure to laser light causes crystal growth which plays a major role in modifying other characteristics of Se80Te10In10 alloy. The comparison of the present results with the literature confirms that laser exposure is a more effective way than the compositional variation approach for tailoring the dielectric properties of the present glass-ceramic sample. © 2023 IOP Publishing Ltd.
Effect of Sn content on some optical properties of Se90Pb10-x thin films
(Elsevier B.V., 2020) Ebraheem O. Hawarat; Mousa M.A. Imran; Omar A. Lafi; Hassan K. Juwhari; Bashar I. Lahlouh; N. Chandel; N. Mehta
Se90Pb10 and Se90Pb8Sn2 thin films of thickness 400 nm were evaporated on glass substrates. The glassy nature of the prepared films was ascertained by differential scanning calorimeter thermograms and X-ray diffraction patterns. Spectra of reflection and transmission of the prepared films were recorded using FilmTek3000 in the wavelength range of 300–900 nm. The absorption coefficient was calculated and used to evaluate the optical band gap energy which comes out to be 2.1 and 2.2 eV for SePb and SePbSn thin films, respectively. The extinction coefficient (k), refractive index (n), real (ε′) and imaginary (ε") dielectric constants were also obtained. Results indicate that the addition of Sn content reduces the value of (n), (ε′) and (ε"), while that of k increases. The observed changes in the studied optical parameters were interpreted depending on the chemical bond approach of Tichy and Ticha. © 2020 Elsevier B.V.
Estimation of Density of Localized States in Amorphous Se80Te20 and Se80Te10M10 (M = Cd, In, Sb) Alloys Using AC Conductivity Measurements
(Springer New York LLC, 2015) N. Chandel; N. Mehta; A. Kumar
The ac conductivity of amorphous Se80Te20 (a-Se80Te20) and amorphous Se80Te10M10 (a-Se80Te10M10) alloys has been measured as a function of temperature and frequency in a low-temperature regime. An analysis of the experimental data confirms that ac conductivity is reasonably well interpreted by the Austin–Mott model. The density of localized states was determined in the low-temperature region from 201 K to 280 K. Possible explanations of “metal-induced effects” on the conduction mechanism of a-Se80Te20 alloy are discussed. © 2015, The Minerals, Metals & Materials Society.
Estimation of Mott parameters in amorphous Se80Te20 and Se80Te10M10 (Cd, In, Sb) alloys
(2011) N. Chandel; N. Mehta; A. Kumar
In the present communication, d.c. conductivity of a-Se80Te 20 and a-Se80Te10M10 (M = Cd, In, Sb) alloys has been studied in the temperature range 225-311 K in order to identify the conduction mechanism and to analyze the effect of different metallic additives on d.c. conduction in a-Se80Te20 alloy below the room temperature. An analysis of the experimental data confirms that conduction in low temperature region is due to variable range hopping in localized states near the Fermi level. The Mott parameters have been calculated in a-Se80Te20 and a-Se80Te10M 10 (M = Cd, In, Sb) alloys. The experimental data is found to fit well with Mott condition of variable range hopping conduction. Crown Copyright © 2011 Published by Elsevier Ltd. All rights reserved.
Explanation of Meyer-Neldel rule in the thermally activated a.c. conduction in some chalcogenide glasses using correlated barrier hopping model
(2012) N. Chandel; N. Mehta
We have investigated Meyer-Neldel rule in thermally activated a.c. conduction for a-Se 80Te 20 and a-Se 80Te 10M 10 (M = Cd, In, Sb) alloys by two different approaches. In the first case, the temperature dependence of a.c. conductivity is studied at different audio frequencies without changing the composition of glassy system. In the second case, the composition itself varies at a particular audio frequency. The results are explained by using wellknown correlated barrier hopping model. © Springer Science+Business Media, LLC 2012.
Investigation of a.c. conductivity measurements in a-Se80Te 20 and a-Se80Te10M10 (M = Cd, in, Sb) alloys using correlated barrier hopping model
(2012) N. Chandel; N. Mehta; A. Kumar
The a.c. conductivity of a-Se80Te20 and a-Se 80Te10M10 (M = Cd, In, Sb) alloys has been investigated as a function of temperature in the range from 280 to 330 K and frequency in the range from 102 to 104 Hz. The experimental results indicate that a.c. conductivity σac is proportional to ωs where s < 1 and decreases with increasing temperature. The results obtained are discussed in terms of the correlated barrier hopping (CBH) model. An agreement between experimental and theoretical results suggests that the a.c. conductivity behavior of a-Se80Te 20 and a-Se80Te10M10 (M = Cd, In, Sb) system can be successfully explained by CBH model. The contribution of single polaron and bipolaron hopping to a.c. conductivity in present alloys is also studied. © 2011 Elsevier B.V. All rights reserved.
Novel explanation for thermal analysis of glass transition
(Elsevier Ltd, 2019) Ankita Srivastava; N. Chandel; Neeraj Mehta
In this work, we have treated the glass transition or pre-crystallization phenomenon as glass/amorphous phase transition. Particularly, we have reported the thermal analysis of so-called glass/amorphous phase transition in recently prepared silver containing semiconducting glasses of third generation (i.e., quaternary system) in terms of glass transition fraction. We have used a state of art DSC technique to understand the glass transition behavior. Present multi-component glasses of SeTeSnAg (STSA) system have been analyzed by using DSC scans at different heating rates. Model-free iso-conversional methods have been used for the study of pre-crystallization kinetics of present glasses. Variation of the glass transition activation energy Eg with the extent of conversion α has been also analyzed. Other significant parameters like rate constant of re-crystallization, order-parameter of pre-crystallization, Hruby number and thermal stability have been determined. We have observed some intimation regarding the conditions of structural change during glass/amorphous phase transition in terms of mode coupling theory. © 2019 Elsevier B.V.
Role of Bi incorporation on glass transition kinetics in glassy Se78Te20Sn2 alloy
(Taylor and Francis Ltd., 2016) H. Kumar; N. Chandel; N. Mehta
In this communication, we report the results of calorimetric measurements on the samples of recently synthesized multi-component glassy alloys of Se78 − xTe20Sn2Bix (0 ≤ x ≤ 6) system. For calorimetric study of glass transition kinetics, differential scanning calorimetry (DSC) technique has been used in non-isothermal mode. Peak glass transition temperature (Tg) is determined using the DSC scans. Kinetic parameters A and B of glass transition are determined using heating rate dependence of Tg. Activation energy of glass transition (Eg) has been calculated using Moynihan and Kissinger methods. Glass-forming ability and thermal stability are also determined using Hurby and Saad–Poulin relations, respectively. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
Study of defect state chemistry of chalcogens elements (Se/Te) in binary Se100-xTex glassy system using lowtemperature d.c. conductivity measurements
(National Institute of Optoelectronics, 2020) Shobhit Saraswat; V.K. Tomar; N. Chandel; N. Mehta
The density of defect states (DDS) has always been a subject of curiosity in electronic materials as the knowledge of this parameter is a key parameter for determining the applications of these materials. Chalcogenide glasses are well known as electronic materials because of their excellent electrical properties (e.g., resistive switching, thermally activated a.c. and d.c. conduction, dielectric relaxation, etc). In the present paper, the d.c. conductivity has been measured for chalcogens elements Se and Te based binary glasses in the low-temperature region to apply the Mott’s theory of electronic conduction. The conduction mechanism in this region follows the Mott’s temperature dependence. The further investigations provide the estimation of the density of defect states (DDS) in Se100-xTex alloys. The value of DDS is decreased with the increase in Te concentration. We have observed a correlation between the DDS and the electronegativity of the chalcogens elements Se and Te. The compositional dependence of the hopping parameters indicates that the condition becomes easier for the variable range hoping with the rise in the Te concentration. © 2020, National Institute of Optoelectronics. All rights reserved.
Study of thermally activated a.c. conduction in a-Se80Te 20 and a-Se80Te19.5M0.5 (M = Cd, In, Sb) alloys
(2011) N. Chandel; N. Mehta; A. Kumar
The temperature and frequency dependence of a.c. conductivity in a-Se 80Te20 and a-Se80Te19.5M 0.5 (M = Cd, In, Sb) alloys have been investigated. Measurements have been carried out for the frequency range 0.5 kHz-10 kHz in the temperature range from room temperature to glass transition temperature. The a.c. conductivity σac is found to be proportional to ωs where s < 1. The temperature dependence of both σac and the parameter s is reasonably well interpreted by the correlated barrier hopping (CBH) model. © 2010 Elsevier Masson SAS. All rights reserved.
Study of thermo-mechanical properties of a-Se80Te20 and a-Se80Te10M10 (M=Cd, In, Sb) alloys
(2013) N. Chandel; N. Mehta
The mechanical properties of chalcogenide glasses play imperative role for their realistic applications and are intimately connected with their structure as well as physical and chemical properties. The paper reports the effect of additives (Cd, In, Sb) on the micro-hardness and related thermo-mechanical properties of glassy Se80Te20 alloy. We have found that that micro-hardness of binary Se80Te20 alloy is changed significantly after the incorporation of Cd, In and Sb additives as chemical modifiers. The other thermo-mechanical parameters like volume (Vh) and formation energy (Eh) of micro-voids in the glassy network and the modulus of elasticity E are also calculated in present glasses. Possible explanations of metal-induced effects on thermo-mechanical properties of glassy Se80Te20 alloy are also discussed. © 2013 Elsevier B.V.
Synthesis and thermal characterization of novel phase change materials (PCMs) of the Se-Te-Sn-Ge (STSG) multi-component system: calorimetric studies of the glass/crystal phase transition
(Royal Society of Chemistry, 2019) Shiv Kumar Pal; N. Chandel; N. Mehta
According to recent literature, germanium-containing chalcogenide glasses (ChGs) show improvement in thermal stability and glass-forming ability because of the self-organization of the glass network towards a more rigid structure. The Ge-containing ChGs play a potential role as PCMs in phase-change optical memory (PCOM) applications. This endeavor reports the synthesis of some novel PCMs with Ge as the chemical modifier to improve the kinetic parameters of glass/crystal phase transition. The compositional variation of the various kinetic parameters in the present STSG chalcogen-rich non-oxide glasses Se 78−y Ge y Te 20 Sn 2 (0 ≤ y ≤ 6) has been studied by means of the state-of-the-art differential scanning calorimetric (DSC) technique in the non-isothermal mode. The thermally assisted glass transition and crystallization phenomena have been investigated by examining the variation in various kinetic parameters like the characteristic kinetic temperatures (glass transition temperature T g , on-set crystallization temperature T o and peak crystallization temperature T c ), the activation energies involved in both phenomena, the thermal stability factor S and the glass-forming ability (GFA). The thermal stability factor S and GFA increase appreciably at higher concentrations of Ge as a signature of stiffness transition followed by the self-organization of the corner-sharing and the edge-sharing arrangements of the GeSe 4 phase. © The Royal Society of Chemistry.
Theoretical prediction of some physical parameters in glassy Se 80Te 20 and glassy Se 80Te 10M 10 (M = Cd, In, Sb) alloys
(2012) N. Chandel; N. Mehta
In the present paper, we have theoretically predicated some significant physical parameters, i.e., coordination number, constraints, density, molar volume, cohesive energy, heat of atomization, etc., for glassy Se 80Te 20 and glassy Se 80Te 10M 10 (M = Cd, In, Sb) alloys. A theoretical study of the glassy Se 80Te 20 and glassy Se 80Te 10M 10 (M = Cd, In, Sb) alloys reveals that there is a significant change in the structural environment of the system due to rigidity percolation. © 2012 EDP Sciences.
Thermal analysis for study of influence of Cd, In, and Sb on glass transition kinetics in glassy Se80Te20 alloy using DSC technique
(2014) N. Chandel; N. Mehta
In this paper, we have incorporated Cd, In, and Sb in glassy Se 80Te20 alloy to see the metal-induced effect of these additives on its glass network and kinetic properties. Specifically, we report results of systematic calorimetric measurements to study the glass transition kinetics. The glass transition behavior of glassy Se80Te20 and glassy Se80Te10M10 (M = Cd, In, Sb) alloys has been analyzed by differential scanning calorimetric technique at various heating rates. The activation energy (E g) of glass transition was determined using different kinetic models. Analysis of experimental data reveals that E g varies with the additive elements. The value of various kinetic parameters such as thermal stability, Hruby number, and fragility index has been calculated in non-isothermal mode. © 2013 Akadémiai Kiadó, Budapest, Hungary.