Kedar Singh

Dhanalakshmi Srinivasan Group of Institutions

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N. S. Saxena

University of Rajasthan

N. Mehta

Banaras Hindu University

Sunil Kumar

Sejong University

A. N. Upadhyay

Temple University

Abhay Kumar Singh

University of Jammu

H. Kumar

Banaras Hindu University

R. S. Tiwari

Banaras Hindu University

Indra Sen Ram

University of Delhi

Ashwani Kumar Singh

Indian Institute of Technology BHU

Rajesh Kumar Singh

Central University of Himachal Pradesh

Cooperative Institutions

Banaras Hindu University

University of Delhi

Dhanalakshmi Srinivasan Group of Institutions

Jawaharlal Nehru University

Council of Scientific and Industrial Research

CSIR National Physical Laboratory of India

Aryabhatta Research Institute of Observational Sciences

University of Rajasthan

Deen Dayal Upadhyaya Gorakhpur University

Indian Institute of Technology BHU

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Structural Origin of Optical Band Edge Shift in Se₇₀Ge_30‐xBi_x (0≤x≤10) Glassy Alloys

ChemistrySelect (2019)

Pankaj Kumar Mishra Aditya N. Upadhyay Kedar Singh H. Kumar

Abstract Bulk glasses of Se−Ge‐Bi system have been prepared by quenching the melt. The XRD exhibits very weak peaks riding over halos. DSC scans show a single stage to a multistage crystallization with an incremental substitution of Ge by Bi, indicating evolution of structurally inhomogeneous phases at the molecular level with the increasing content of Bi. The Raman spectra (50‐500 cm‐1) reveal the formation of the corner and edge‐sharing GeSe 4/2 terahedral and Bi 2 Se 3 pyramidal units. Transmission electron microscope (TEM) Images depicts the formation of submicron to nano‐sized spherical shaped structural units in a chain‐like configuration. Fragmentation of chains and refinement effect of Bi are noticed in TEM and SEM Images. The optical absorption edge found to be red‐shifted along with a sharp decrease in optical band gap (1.74‐0.82), with the increasing fraction of Bi in alloys. Attempts have been made to elucidate the results on the structural considerations (bond and band diagram) and Burstein‐Moss effect.

Absorption edge

Branching (polymer chemistry)

10.1002/slct.201900104

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THERMO-PHYSICAL PROPERTIES OF Se-Te-Sb VITREOUS CHALCOGENIDE SEMICONDUCTORS

P. Krishna Kumar Kedar Singh

Measurements of thermo-physical properties such as effective thermal conductivity (λe) and effective thermal diffusivity (χe) of Se85-xTe15Sbx (at x = 2, 4, 6, 8 and 10) chalcogenide glasses have been made with the help of Transient Plane Source (TPS) technique at room temperature. We have calculated phonon mean free path (τ) and thermal effusivity (e) of Se85-xTe15Sbx (at x = 2, 4, 6, 8 and 10) chalcogenide glasses form the measured values of effective thermal conductivity (λe) and effective thermal diffusivity (χe). In the present study the variation of thermo-physical properties i.e. effective thermal conductivity (λe), effective thermal diffusivity (χe), phonon mean free path (τ) and thermal effusivity (e) has been plotted as the function of average co-ordination number which decides the stability of these glasses at different Sb at wt%. The measured values of the effective thermal conductivity (λe), and of the effective thermal diffusivity (χe) show maxima because the chain length is maximum, hence phonon mean free path is maximum at = 2.06. Thermal effusivity (e) shows its minimum at = 2.06 because of non availability of large number of degree of freedom to exchange the thermal energy with surroundings.

Thermal effusivity

Thermal conductivity measurement

Chalcogenide glass

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Observation of inverse Meyer–Neldel rule in thermally activated crystallization of a hybrid composite of phenol formaldehyde

The Philosophical Magazine A Journal of Theoretical Experimental and Applied Physics (2009)

N. Mehta Kedar Singh Sunil Kumar

We report the inverse Meyer–Neldel (MN) rule in the thermally activated crystallization of a hybrid composite of phenol formaldehyde using two experimental approaches. In the first experiment, the annealing time dependence of the pre-exponential factor K 0 and the activation energy of crystallization E c were studied. In the second experiment, the annealing temperature dependence of the same parameters was investigated. We observed the inverse Meyer–Neldel rule between the pre-exponential factor K 0 and the activation energy of crystallization E c in both cases.

Inverse temperature

10.1080/14786430902755032

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Effect of Pb additive on crystallization kinetics of Se80In20 glassy matrix

Physica B Condensed Matter (2012)

Indra Sen Ram Kedar Singh

Isothermal process

Chalcogenide glass

10.1016/j.physb.2012.05.004

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Effect of indium additive on glass-forming ability and thermal stability of Se–Zn–Te chalcogenide glasses

Philosophical Magazine Letters (2010)

Abhay Kumar Singh N. Mehta Kedar Singh

Abstract We report the measurements on Se93− x Zn2Te5In x (0 ≤ x ≤ 10) chalcogenide glasses using differential scanning calorimetry. The thermal stability and glass forming ability of these glasses are studied by different criteria. The composition dependence of the various kinetic parameters of crystallization is discussed. Keywords: thermal stabilityactivation energydifferential scanning calorimetryphase transitionsnon-isothermal crystallizationchalcogenide glasses Acknowledgements Authors are thankful to the University Grants Commission (UGC), New Delhi, for providing financial support under UGC Project No. 33-40/2007SR.

Chalcogenide glass

Thermal Stability

10.1080/09500830903571376

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Citations (25)

Effective thermal conductivity and effective thermal diffusivity of Se100 ? xZnx chalcogenide system

Journal of Materials Science (2005)

N. S. Saxena Rahul Sharma Kedar Singh T.P. Sharma

10.1007/s10853-005-6119-x

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Citations (2)

THERMAL TRANSPORT IN Se81Te15Sb4 CHALCOGENIDE GLASS

P. Krishna Kumar Kedar Singh

Measurement of effective thermal conductivity (λe) effective thermal diffusivity (χe) of Se81Te15Sb4 thin pellets prepared under a load of 5 tons is carried out in the temperature range 25 C to 85 C using the transient planar source (TPS) technique. In the heating process the modification of λe and χe isobserved . Both quantities are found toreqach a maximum at 65 C, which lies in the vicinity of the glass transition temperature. During the cooling process λe and χe remain the same at all temperatures. Such behaviour proves the thermal hysteresis in the sample, which can be explained on the basis of the structural changes in the material.

Thermal conductivity measurement

Atmospheric temperature range

Transient (computer programming)

Hysteresis

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Layered Sb2Te3 Nanoflakes as Chalcogenide Dielectrics

Journal of Electronic Materials (2013)

Punita Srivastava Kedar Singh

Dielectric loss

High-κ dielectric

10.1007/s11664-013-2640-x

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Citations (4)

Electrical conduction mechanism in Se90-xTe5Sn5Inx (x = 0, 3, 6 and 9) multi-component glassy alloys

AIP Advances (2015)

Indra Sen Ram Sunil Kumar Rajesh Kumar Singh Prabhakar Singh Kedar Singh

Electrical conductivity of Se90-xTe5Sn5Inx (x = 0, 3, 6 and 9) glassy systems was studied employing impedance spectroscopic technique in the frequency range 100 Hz to 1 MHz and in the temperature range 308-388 K. The DC conductivity (σdc) at each temperature was evaluated from the low frequency plateau region for all the samples under investigation. The bulk conductivity for each sample was also evaluated from Nyquist impedance plots. The semicircle shape of Nyquist plot exhibit dipolar nature of samples. The activation energy for glassy, amorphous and crystalline region from the Arrhenius plot of the DC conductivity and bulk conductivity was evaluated. From the results it is found that activation energy varied from 0.091 to 0.194 eV in glassy, 0.686 to 0.002 eV in amorphous and 0.215 to 0.503 eV in crystalline region. The activation energy (ΔE) from DC conductivity and bulk conductivity found to be close in corresponding regions. The pre-exponential factor was also calculated for all three regions.

Nyquist plot

Arrhenius plot

Atmospheric temperature range

10.1063/1.4929577

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Citations (17)

Electrical And Dielectric Properties Of Carbon Nanotube Containing Se85Te10Ag5 Glassy Composites

Advanced Materials Letters (2015)

A. N. Upadhyay R. S. Tiwari Kedar Singh

The electrical and dielectric properties of 3 and 5 wt. % of multi-walled carbon nanotube (MWCNT) containing Se85Te10Ag5 glassy composites have been investigated in the frequency range 20 Hz to 2 MHz from room temperature to 387 K. It has been found that the electrical conductivity is enhanced by 6 to 9 orders of magnitude up to 5 wt. % of MWCNT content resulting in transition for insulating to conducting behaviour. The activation energies for all samples have also been evaluated from the Arrhenius plot of the DC conductivity which shows a decreasing trend up to 5 wt. % MWCNT content. The largest dielectric constant of 142 (almost 10 times greater than pristine Se85Te10Ag5 glassy alloy) has been observed for 5 wt. % of MWCNT content at room temperature in low frequency range. Therefore it can be inferred that the electrical and dielectric properties of the chalcogenide glasses can be altered by the admixing or doping of carbon nanotubes (CNTs). The enhanced dielectric constant and electrical conductivity can be attributed to interface effect between MWCNT and the glassy matrix.

Smart material

10.5185/amlett.2015.5978

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Citations (8)