avnagar University

Bhāvnagar, India

avnagar University

Bhāvnagar, India
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Astik N.,M. S. University of Baroda | Patil S.,avnagar University | Jha P.K.,M. S. University of Baroda
AIP Conference Proceedings | Year: 2016

Nanocrystalline stoichiometric La0.7Sr0.3MnO3 (x=0.3) manganites have been synthesized through solid-state reaction by ball milling mechanical method at two different sintering temperatures 1250°C and 1350°C. The synthesized samples were characterized using X-ray diffraction (XRD) and found to have rhombohedral crystal structure (R-3c). The calcined samples exhibited a pure single phase perovskite, had a crystallite size of about 47-51 nm. The morphology of the prepared nanocrystalline manganites were recorded by the field emission gun-scanning electron microscope (FEG-SEM) and EDAX. © 2016 Author(s).

Patil S.S.,avnagar University | Jha P.K.,M. S. University of Baroda | Bhargava P.,Indian Institute of Technology Bombay
AIP Conference Proceedings | Year: 2015

In this paper, the effect of sintering temperature on the structural properties of Sr doped lanthanum manganites is studied. The Sr doped manganites are synthesized using solid state reaction method. The structural properties of the sintered powders are examined by X-ray diffraction. The La0.9Sr0.1MnO3 powder samples exhibit a dominant peak along with increased peak intensity corresponding to the (104), (202), (204) reflections and some new peaks also appeared along (116),(036) and (0210) reflections compared to first sintering temperature (1250°C). This confirms a more polycrystalline nature of the powder at higher sintering temperature. The crystallite size varies between 45 nm to 50 nm. For relative study, the calculated average crystallite size and lattice parameters are noted in tabulated form. © 2015 AIP Publishing LLC.

Dabhi S.D.,avnagar University | Shrivastava D.,Barkatullah University | Jha P.K.,M. S. University of Baroda | Sanyal S.P.,Barkatullah University
Physica C: Superconductivity and its Applications | Year: 2016

The electronic, phonon structure and superconducting properties of tin antimonide (SnSb) in rock-salt (RS) structure are calculated using first-principles density functional theory. The electronic band structure and density of states show metallic behavior. The phonon frequencies are positive throughout the Brillouin zone in rock-salt structure indicating its stability in that phase. Superconductivity of SnSb in RS phase is discussed in detail by calculating phonon linewidths, Eliashberg spectral function, electron-phonon coupling constant and superconducting transition temperature. SnSb is found to have a slightly lower TC (3.1 K), as compared to SnAs. © 2016

Shrivastava D.,Barkatullah University | Dabhi S.D.,avnagar University | Jha P.K.,M. S. University of Baroda | Sanyal S.P.,Barkatullah University
Solid State Communications | Year: 2016

Pressure induced structural phase transitions in SnAs and SnSb have been studied using ab-initio density functional theory. The phase transition from NaCl to CsCl structure occurs at 29.8 GPa for SnAs, which agrees well with experimental data, while the same for SnSb is found to be 10.6 GPa, reported for the first time. The calculated ground state properties are in good agreement with available experimental and theoretical results. The electronic and bonding properties have also been analyzed. The elastic constants along with other secondary elasticity properties in B1 (NaCl-type) phase are also estimated at ambient as well as high pressure. © 2016 Elsevier Ltd. All rights reserved.

Mankad V.,avnagar University | Jha P.K.,avnagar University | Ravindran T.R.,Indira Gandhi Center for Atomic Research
Journal of Applied Physics | Year: 2013

Polarized and depolarized spectra from gold (Au) nanoparticles of different sizes are investigated in the small size range, between 3 and 7 nm, using low frequency Raman spectroscopy. Acoustic vibrations of the free-standing Au nanoparticles are demonstrated with frequencies ranging from 5 to 35 cm -1, opening the way to the development of the acoustic resonators. A blue shift in the phonon peaks along with the broadening is observed with a decrease in particle size. Comparison of the measured frequencies with vibrational dynamics calculation and an examination as from the transmission electron microscopy results ascertain that the low frequency phonon modes are due to acoustic phonon quantization. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar (l = 2) vibrations of the spheroidal mode due to plasmon mediated acoustic vibrations in Au nanoparticles. © 2013 American Institute of Physics.

Mankad V.H.,avnagar University | Jha P.K.,M. S. University of Baroda
Journal of Thermal Analysis and Calorimetry | Year: 2016

To understand the thermal behavior of superhard uranium carbide (UC), in the present work thermodynamic properties of UC in rock-salt structure are investigated using first-principles plane-wave pseudopotential method within the density functional theory. Thermodynamic functions such as specific heat, entropy, internal energy and enthalpy as a function of temperature have been calculated using the phonon dispersion curves and phonon density of states within quasi-harmonic approximation. The variation of lattice specific heat with temperature is also compared with available experimental data. The dependence of selected observations of UC compounds on the effective U parameter has also been investigated. The DFT + U calculation is performed in order to describe precisely the strong on-site Coulomb repulsion incorporation of Hubbard parameter U = 3.0 eV that leads to better comparison of lattice parameter and elastic constants with experimental and available theoretical data. The calculated phonon frequencies and elastic constants show that the UC in rock-salt structure is dynamically and mechanically stable at ambient condition as indicated by their positive values. The temperature dependence of thermal and electrical conductivities has also been calculated and compared with the available experimental data and discussed. The possible use of UC in thermoelectric devices using thermal conductivity and resistivity is also discussed, and the present study suggests that the UC can be a potential candidate for the thermoelectric application at higher temperatures. We hope that the present study should stimulate further studies of this material. © 2015 Akadémiai Kiadó, Budapest, Hungary.

Mir S.H.,Central University of Gujarat | Jha P.C.,Central University of Gujarat | Dabhi S.,avnagar University | Dabhi S.,M. S. University of Baroda | Jha P.K.,M. S. University of Baroda
Materials Chemistry and Physics | Year: 2016

The present work reports a comprehensive study of structural, dielectric, lattice dynamic and thermodynamic properties of magnesium chalcogenides MgX (X = S, Se, and Te) in rock-salt, zinc-blende and wurtzite crystal structures. Density functional theory calculations were performed using Perdew-Burke-Ernzerhof (PBE) functional (hereafter, PBE) and along with van der Walls interactions (hereafter, DFT-D). Our calculations show that the inclusion of van der Walls interactions improves the results and predict structural parameters close to the experimental values than using PBE functional alone. Both approaches show that the rock-salt phase is the ground state stable phase of MgS. The DFT-D calculations indicate that rock-salt whereas PBE results show wurtzite as the stable crystal structure for MgSe and MgTe respectively. Further, density functional perturbation theory has been employed to obtain the phonon dispersion curves and phonon density of states. The present phonon calculations show that these compounds are dynamically stable in the three considered phases. Thereafter, temperature dependent heat capacity at constant volume and entropy are also presented and discussed. © 2016 Elsevier B.V.

Gupta S.K.,avnagar University | Gupta S.K.,Michigan Technological University | Gupta S.K.,St Xaviers College | Gupta S.D.,avnagar University | And 3 more authors.
Materials Chemistry and Physics | Year: 2014

The present paper reports the structural, electronic, phonon and thermodynamical properties of some transition-metal nitrides (TMN: TiN, VN and CrN) by means of first-principles calculations. The computed equilibrium lattice constant and bulk modulus agree well with the available experimental and theoretical data. The electronic band structure and density of states calculations show metallic nature. The phonon frequencies are positive throughout the Brillouin zone for these compounds in rocksalt structure indicating dynamical stability. The calculated electron-phonon coupling constant λ and superconducting transition temperature agree reasonably well with the available experimental data. These compounds behave as a conventional phonon-mediated superconductor. Within the GGA and quasi-harmonic approximation, thermodynamical properties are also investigated. © 2013 Elsevier B.V. All rights reserved.

Astik N.M.,avnagar University | Baldha G.J.,Saurashtra University
Advanced Materials Research | Year: 2014

The mineral having chemical compositional formula MgAl2O4 is called “spinel”. The ferrites crystallize in spinel structure are known as spinel-ferrites or ferro-spinels. The spinel structure has an fcc cage of oxygen ions and the metallic cations are distributed among tetrahedral (A) and octahedral (B) interstitial voids (sites). A compound of Co0.85Ca0.15-yMgyFe2O4 (y=0.05, 0.10, 0.15) is synthesized in polycrystalline form, using the stoichiometric mixture of oxides with conventional standard ceramic technique and characterized by X-ray diffraction (XRD). The XRD analysis confirmed the presence of cubic structure. The intensity of each Bragg plane is sensitive to the distribution of cations in the interstitial voids of the spinel lattice. The computer program Powder X software for XRD analysis has been utilized for this purpose. The compositions of Co0.85Ca0.15-yMgyFe2O4 (y=0.05, 0.10, 0.15) ferrites have been prepared by standard ceramic method with double sintering at 9500C, 11000C. In present study, we report the structural, electrical and magnetic properties of above said compound. © (2014) Trans Tech Publications, Switzerland.

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