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Okram G.S.,UGC-DAE Consortium for Scientific Research | Kaurav N.,Government Holkar Science College | Lalla N.P.,UGC-DAE Consortium for Scientific Research
Faraday Discussions | Year: 2015

Nickel nanoparticles (NPs) of different shapes and sizes in polydispersed as well as monodispersed forms were synthesized using trioctylphosphine (TOP), triphenylphosphine (TPP), oleylamine (OA) and their combinations as surfactants to study their self-assembly inducing capabilities. Randomly agglomerated polydispersed NPs were found for TPP and OA, and TPP or OA separately. However, in consolidation with the earlier report of Singh et al., J. Mater. Chem. C, 2014, 2, 8918, NPs formed using TOP only and a combination of TOP with OA naturally exhibited monodispersed NPs associated with natural nanolattice formation without any other external force or surfactants, demonstrating clearly the self-inducing capacity of TOP into monodispersed NPs and their self-assembled nanolattices. Fourier-transformed infra-red (FTIR) data clearly indicated the capping of these surfactants along with acetylacetonate ligands from nickel acetylacetonate precursor on the surface of the NPs. Remarkably, the narrowest zeta potential (ζ) base-widths were observed for samples possessing a self-assembled nanolattice, compared to the broader ones for randomly agglomerated particles. This journal is © The Royal Society of Chemistry 2015.

Kaurav N.,Government Holkar Science College | Lalla N.P.,UGC-DAE Consortium for Scientific Research | Okram G.S.,UGC-DAE Consortium for Scientific Research
Journal of Materials Chemistry C | Year: 2014

This is the first report on the critical nature of nanolattice formability of different particle sizes (∼4-10 nm) of monodispersed nickel nanoparticles. They exhibit strikingly hexagonal close-packed (hcp) nanolattices without extra forces whenever trioctylphosphine (TOP) is one of the surfactant(s). This clearly establishes the unique role of nanolattice formability of TOP. The c/a ratios are interestingly identical to those of atomic lattices. An attempt has also been made to explain them based on the balanced attractive and repulsive forces of the surfactant-generated cation-anion pairs on the surface of the nanoparticles. The present findings therefore will provide a far-reaching vista for the fabrication of varieties of natural nanolattices and their understanding on applications in a new paradigm. This journal is © the Partner Organisations 2014.

Varshney D.,Devi Ahilya University | Mansuri I.,Devi Ahilya University | Kaurav N.,Government Holkar Science College | Lung W.Q.,National Dong Hwa University | Kuo Y.K.,National Dong Hwa University
Journal of Magnetism and Magnetic Materials | Year: 2012

The effect of Ce-doping on structural, magnetic, electrical and thermal transport properties in hole-doped manganites La 0.7-xCe xCa 0.3MnO 3 (0.0≤x≤0.7) is investigated. The structure of the compounds was found to be crystallized into orthorhombically distorted perovskite structure. dc Susceptibility versus temperature curves reveal various magnetic transitions. For x≤0.3, ferromagnetic regions (FM) were identified and the magnetic transition temperature (T C) was found to be decreasing systematically with increasing Ce concentration. The electrical resistivity ρ(T) separates the well-define metal-semiconducting transition (T MS) for low Ce doping concentrations (0.0≤x≤0.3) consistent with magnetic transitions. For the samples with 0.4≤x≤0.7, ρ(T) curves display a semiconducting behavior in both the high temperature paramagnetic (PM) phase and low temperature FM or antiferromagnetic phase. The electron-phonon and electron-electron scattering processes govern the low temperature metallic behavior, whereas small polaron hopping model is found to be operative in PM phases for all samples. These results were broadly corroborated by thermal transport measurements for metallic samples (x≤0.3) in entire temperature range we investigated. The complicated temperature dependence of Seebeck coefficient (S) is an indication of electron-magnon scattering in the low temperature magnetically ordered regime. Specific heat measurements depict a broadened hump in the vicinity of T C, indicating the existence of magnetic ordering and magnetic inhomogeneity in the samples. The observation of a significant difference between ρ(T) and S(T) activation energies and a positive slope in thermal conductivity κ(T) implying that the conduction of charge carriers were dominated by small polaron in PM state of these manganites. © 2012 Elsevier B.V. All rights reserved.

Mansuri I.,Devi Ahilya University | Varshney D.,Devi Ahilya University | Kaurav N.,Government Holkar Science College | Lu C.L.,National Dong Hwa University | Kuo Y.K.,National Dong Hwa University
Journal of Magnetism and Magnetic Materials | Year: 2011

The magnetic, electrical and thermal properties in the La 0.5-xLnxCa0.5-ySryMnO3 (Ln=Pr, Nd, Sm) bulk system were investigated. Detailed dc magnetization and linear ac susceptibility measurements reveal that the samples first undergo phase transition from paramagnetic to ferromagnetic phase and then to an antiferromagnetic phase upon further cooling. It is found that both the Curie and Neel temperatures decrease systematically with increasing A-site disorder in these manganites. The electrical resistivity exhibits semiconducting behavior throughout the temperature range investigated and the electronic conduction mechanism can be conveniently described within the framework of the variable range hopping model above T=150 K. The Seebeck coefficient (S) in the magnetically ordered regime infers that the complicated temperature dependence of S is an indication of electronmagnon scattering. Specific heat measurements depict a broadened hump in the vicinity of TC, indicating the existence of magnetic ordering and magnetic inhomogeneity in the samples. The temperature dependence of thermal conductivity, κ(T), reveals a positive dκ/dT in the paramagnetic region, which may be related to the local anharmonic lattice distortions associated with small polarons. © 2010 Elsevier B.V.

Kaurav N.,Government Holkar Science college | Choudhary K.K.,Department of National Defence
Advanced Materials Research | Year: 2014

Thermal conductivity κ(T) of LaFeAsO is theoretically investigated below the spin density wave (SDW) anomaly. The lattice contribution to the thermal conductivity (κph) is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and relaxation time below 150 K. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity dominates in LaFeAsO and is an artifact of strong phonon-impurity and - phonon scattering mechanism. Our result indicates that the maximum contribution comes from phonon scatters and various thermal scattering mechanisms provide a reasonable explanation for maximum appeared in κ (T). © (2014) Trans Tech Publications, Switzerland.

Singh J.,IPS Academy | Kaurav N.,Government Holkar Science College | Ganesan V.,UGC-DAE Consortium for Scientific Research | Okram G.S.,UGC-DAE Consortium for Scientific Research
AIP Conference Proceedings | Year: 2014

We demonstrate here a very noteworthy nature of the critical roles of type of cappants, in addition to the particle size, on the electrical resistivity of compacted pellets of nickel nanoparticles (Ni-NPs) in the temperature range from 5 to 300 K that deviate significantly from highly conducting nature of a good metal yet without much deviation of the slopes. For this, face-centered cubic structured Ni-NPs of average particle size ranging from 18 to 33 nm were prepared using different polyol methods in the presence of various additional capping agents. © 2014 AIP Publishing LLC.

Okram G.S.,UGC-DAE Consortium for Scientific Research | Kaurav N.,Government Holkar Science College
Journal of Applied Physics | Year: 2011

Nanocrystalline copper (NC-Cu) of average particle size (D) ranging from 29 to 55 nm was prepared using the polyol method. The compacted pellets of these nanoparticles were investigated using electrical resistivity (ρn) and thermopower (Sn) measurements in the temperature range from 5 to 300 K. The observed electrical resistivity and thermopower data for all the samples are typical of a good metal and the ρn(T) data are analyzed in the framework of the Bloch-Grüneisen theory. Our analysis indicates systematic departure from the bulk property for NC-Cu samples, decreasing effective Debye temperature, exponential decay of both the residual resistivity ratio (RRR) and the temperature coefficient of resistivity [α = (1/ρ)dρ/dT] as D decreases, yet the Boltzmann theory of electron transport still holds true (kFl ≫ 1). Further, the validity of the Nordheim-Gorter rule is also discussed. The temperature dependence of S n is found to be quite sensitive as compared to bulk thermopower SBulk behavior, revealing the evolution of Sn and exhibiting a significant enhancement of the phonon drag peak as D decreases. The present findings overall suggest the significant influence of the grain boundaries, surface atoms, and phonon confinement. © 2011 American Institute of Physics.

Kaurav N.,Government Holkar Science College
Physica Scripta | Year: 2013

Pressure-induced structural aspects of ZnS-type (B3) to NaCl-type (B1) structure in XC (X = Si, Ge, Sn and Pt) compounds are presented. An effective interionic interaction potential with long-range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction up to second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge is developed. Particular attention is devoted to evaluate the vdW coefficients following the Slater-Kirkwood variational method, as both the ions are polarizable. Our results on vast volume discontinuity in pressure volume phase diagram identify the structural phase transition from B3 to B1 structure. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data. The variations of elastic constants with pressure follow a systematic trend identical to that observed in other compounds of ZnS and NaCl-type structure family and the Born relative stability criteria are valid in XC compounds. © 2013 The Royal Swedish Academy of Sciences.

Kumar C.S.,Government Holkar Science College
Disaster Advances | Year: 2011

Topographical maps are indispensable tools for geologists, geographers, foresters, civil engineers, military personnel etc. The process of finding the sheet numbers for irregular polygons like district boarders, watershed boundaries etc. is bit tedious and cumbersome. With the launching of websites like Google Earth and ISRO Bhuvan, finding the latitudes and longitudes of the points and areas of interest has become very easy. Further geo-referenced data in popular GIS software formats are also available from other sources. Recently Survey of India has brought out Open Series Maps (OSMs) on WGS-84 Datum, which have slightly different numbering system than that of the Topographical maps on Everest Datum. Keeping this in mind, an interactive computer programme has been developed for quick and accurate calculation of number of both Topographical Maps and OSMs published by Survey of India. The data input and output are compatible with popular GIS file formats like shape and KML.

Choudhary K.K.,Shri Vaishnav Institute of Technology and Science | Kaurav N.,Government Holkar Science College
Journal of Physics: Conference Series | Year: 2012

Quantitative analysis of the optical conductivity σ(ω) for the normal state of Iron-Based superconductors CeOFeAs have been made within the two-component scheme: one is the coherent Drude free carrier excitations and other is incoherent motion of carriers leading to a polaron formation, originated from inter and intra layer transitions of charge carriers. The model successfully accounts for the anomalies reported in the optical measurements for metallic state of the superconductors. The frequency dependent relaxation rates are expressed in terms of memory functions and the coherent Drude carriers from the effective interaction potential leads to a sharp peak at zero frequency which is an indication of metallic conduction and a long tail at higher frequencies, i.e. in the infrared region. While to that the hopping of carriers from Fe to Fe in the FeAs layer and from FeAs layer to CeO layer (incoherent motion of carriers) yields two-peak value around 100 cm -1 and 425 cm -1 respectively in the optical conductivity centred at mid-infrared region. Both the Drude and hopping carriers contribute to the optical process of conduction in the iron-based superconductors and shows similar results on optical conductivity in the mid-infrared as well as infrared frequency regions as those revealed from experiments. © Published under licence by IOP Publishing Ltd.

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