Browsing by Author "Namrata Chandel"

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Analysis of physicochemical properties in covalent network chalcogenide glasses (ChGs): critical review of theoretical modeling of chemical bond approach
(Springer Nature, 2019) Namrata Chandel; Neeraj Mehta
The Group 16 elements are frequently named as chalcogens (‘ore builders’). From the geographical point of view, they are known as chalcophiles which are the soft elements (keeping in mind the terminology of the hard/soft acids and bases concept). In the geographical sense, chalcophiles preferably form minerals with sulfur (S), selenium (Se) and tellurium (Te). However, oxygen (O) tends to bind preferably to lithophiles, which are hard elements such as the alkali metals, early transition metals, and silicon. The special position of oxygen amongst the chalcogen elements is its association with its very high electronegativity, which in turn correlates with its high ionization energy and the small atomic radius; which makes it difficult for oxygen to act as a central atom in electron-rich multicentre bonds. In the present script, we have reviewed the models for theoretical prediction of some significant physical parameters i.e. coordination number, constraints, density, molar volume, cohesive energy and heat of atomization etc. for the three generations of Se rich multi-component glasses are presented. The present theoretical study of the multi-component chalcogenide glasses reveals that there is a significant change in the structural environment of the three generations (binary, ternary and quaternary systems) due to rigidity percolation. © 2019, Springer Nature Switzerland AG.
Calorimetric studies of crystallization for multi-component glasses of Se–Te–Sn–Ag (STSA) system using model-free and model-fitting non-isothermal methods
(Springer Netherlands, 2017) Ankita Srivastava; Namrata Chandel; Neeraj Mehta
Silver-containing chalcogenide glasses are well-known candidates for technical applications as well as for the fundamental studies. In the present report, we have studied the kinetics of glass/crystal phase transformation in novel synthesized glasses of STSA system. For this, purpose, differential scanning calorimetric technique has been employed at four different heating rates (5, 10, 15, 20 K min−1). This paper explores the thermal analysis of calorimetric data using both advanced iso-conversional methods for the determination of effective activation energy as a function of extent of crystallization and classical non-isothermal methods for the determination of over-all crystallization activation energy. Iso-conversional methods, such as Kissinger–Akahira–Sunose method and Flynn–Wall–Ozawa method, have been used to study the variation of activation energy of crystallization and other kinetic parameters with extent of crystallization. Non-isothermal methods (Kissinger method, Augis–Bennett method, and Matusita–Sakka method) have been used to determine over-all activation energy of crystallization and other significant parameter of thermally activated crystallization. We have also explained the composition dependence of various kinetic parameters. © 2016, Akadémiai Kiadó, Budapest, Hungary.
Comprehensive studies of temperature and frequency dependent dielectric and a.c. conducting parameters in third generation multi-component glasses
(Royal Society of Chemistry, 2018) Namrata Chandel; M.M.A. Imran; Neeraj Mehta
The dielectric relaxation and thermally assisted a.c. conduction play an important role in understanding the conduction mechanism in chalcogenide glasses. These two phenomena are often the deciding factors of the suitability of chalcogenide materials for particular device applications. Dielectric relaxation studies are important to understand the nature and origin of dielectric losses, which, in effect, may be useful in the determination of structure and defects in solids. The study of thermally assisted a.c. conduction can be used as a tool to understand the nature of defect states and the estimation of their density of defect states. In this paper, therefore, we have studied the metal-induced effects of cadmium (Cd), indium (In) and antimony (Sb) on dielectric relaxation and thermally activated a.c. conduction in ternary Se80Te18Sn2 glass. The density of charged defect states in quaternary Se80Te8Sn2M10 alloys is found to vary with the electro-negativity difference (ξM - ξTe) of the foreign element M and Te. Further analysis shows that the increasing sequence of the density of charged defects is explained in terms of variation in the lone-pair electrons after the incorporation of Cd, In and Sb. © The Royal Society of Chemistry 2018.
Correlation between structural and thermodynamic properties of some selenium based phase-change materials
(Elsevier Ltd, 2018) Namrata Chandel; Neeraj Mehta
In this study, we prepared novel selenium rich multi-component glasses by incorporating In, Cd and Sb as foreign elements in an Sn containing Se[sbnd]Te system in order to study their metal-induced effects on the thermal properties of the parent ternary glass. In particular, we determined the thermodynamic parameters of Se80Te18Sn2 and Se80Te8Sn2M10 (M = Cd, In, Sb) glassy semiconductors in a non-isothermal environment using the differential scanning calorimetry. Calorimetric measurements were obtained in the glass transition regions for Se80Te18Sn2 and Se80Te8Sn2M10 (M = Cd, In, Sb) glasses to determine their thermodynamic parameters such as the specific heat, enthalpy, and entropy during glass transition. We analyzed the variation in the specific heat before and after the heat capacity jump in these alloys. The metal-induced effects of foreign elements on the thermodynamic properties of the parent glass were also investigated in terms of the influence of the elemental specific heat of the added elemental metal as well as the thermal stability and glass-forming ability of the glasses. © 2017 Elsevier Ltd
Iso-conversional kinetic analysis of quaternary glass re-crystallization
(Elsevier Ltd, 2017) Ankita Srivastava; Namrata Chandel; Neeraj Mehta
Iso-conversional kinetic analysis is popular in scientific community for analyzing solid-state reactions (e.g., glass/amorphous and amorphous/crystal phase transformations, re-crystallization etc). It is a recognized significant tool to achieve useful outcomes for the solid state reaction under consideration. Present work is devoted to explore some insights of thermally activated crystallization using various heating rates (VHR) method. We have examined the correlation between iso-conversional activation energy and iso-conversional rate of crystal growth. In fact, we have observed the compensation law and iso-kinetic relationship using two different approaches for the study of crystallization phenomenon that drives thermally in an Arrhenian manner. Moreover, we found that the estimated intercepts and gradients (i.e., Meyer-Neldel energy and Meyer-Neldel pre-factor respectively) for both approaches also vary linearly and both sets are remarkably identical. These results approach to an inference for ensuring the equivalence of compensation law and iso-kinetic relationship and provide an understanding of various advanced materials in physical chemistry, materials sciences and solid-state physics. © 2017
Kinematics of glass to crystal phase transformation in novel multi-component glassy Se-Te-Sn-M (M = Sb, In, Cd) alloys; [Cinemática de la transformación de fase de vidrio a cristal en nuevas aleaciones vítreas multicomponente Se-Te-Sn-M (M = Sb, In, Cd)]
(Sociedad Espanola de Ceramica y Vidrio, 2022) Namrata Chandel; Neeraj Mehta; Alaa Dahshan
The kinetics of the thermally induced glass / crystal phase transformation of chalcogenide glasses plays an important role in determining their candidacy for optical phase change memory applications. The rate of crystallization and the corresponding activation energy are the two crucial kinetic parameters that reflect the durability and quality (i.e., storage properties) of phase change materials. This script deals with metal-induced effects on thermally regulated non-isothermal crystallization in a new glass alloy of Se-Te-Sn using calorimetric measurements. The elements Antimony (Sb), Cadmium (Cd) and Indium (In) have been used as structural modifiers for this purpose. The crystallization and glass transition kinetics of these glass alloys have been investigated by thermal analysis of several kinetic parameters such as the parameter of order n, the maximum crystallization temperature Tc, the crystallization rate K and the consequent activation energy Ec). A DSC is used in non-isothermal mode for the present studies. The values of the activation energy Ec are determined using the data obtained from the displacement of the exothermic peaks of crystallization in non-isothermal DSC plots at various heating rates. The role of the additives Sb, Cd and In in the variation in the rate of crystallization K of and the Avrami index (n) for each glass alloy is also examined. Detailed thermal analysis of the kinetic data confirms the superiority of Cd over the other two additives (In and Sb) for optimization of the kinetic properties of the main SeTeSn glass. © 2021 SECV.
Thermal Kinetics Through Differential Scanning Calorimetry in Chalcogenide Glassy Semiconductors
(Springer Science and Business Media Deutschland GmbH, 2024) Ankita Srivastava; Chandrabhan Dohare; Ritesh Kumar Chourasia; Neeraj Mehta; Namrata Chandel; Dinesh Pathak; Amodini Mishra; Dhirendra Sahoo
Differential Scanning Calorimetry (DSC) is one of the best ways to examine the thermal kinetics of non-equilibrium nature of synthesized non-crystalline materials. The exact thermal kinetics of glassy materials during the glass transition, involves crystallization and polymorphic transition. DSC, a characteristic technique of thermal phase transitions, evolves in the micro-structural properties. The endothermic (glass transition, Tg) and exothermic (crystallization temperature, Tc) nature of chalcogenide glasses obtained during the DSC thermal scanning have been investigated. The phenomenon of crystallization and glass transition kinetics of glassy semiconductors has been deliberated at various different heating rates using differential DSC. The present work deals with model fitting and model free non-isothermal (Kissinger–Akahira–Sunose, Ozawa-Flynn-Wall, Starink and Tang) approaches that are used to determine the various kinetic parameters i.e., activation energy (crystallization, Ec and glass transition, Eg), fraction of crystallization, pre-exponent factor etc. of the growing generations of Chalcogenide glassy binary, ternary, quaternary and multi-component alloys. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.