Publications (17)16.55 Total impact
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Article: Magneto-resistance, thermal conductivity, thermo-electric power and specific heat of superconductor Gd0.95Pr0.05Ba2Cu2.94M0.06O7-[delta] (M=Fe, Ni, Zn and Mn)
Solid State Communications. 09/2011; 151:1117-1121. -
Article: Negative thermoelectric power of over-doped Bi2Sr2CaCu2O8 superconductor
Physica C: Superconductivity. 12/2010; 470:S203-S204. -
Article: The unusual electrical response in polyaniline-threonine composites
Materials Letters. 09/2010; 64:2009-2011. -
Article: Effect of Mn substitution on the thermo-power of the superconductor Mg1−xMnxB2
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ABSTRACT: In this communication a systematic study has been made on the effect of Mn substitution on the thermo-power of MgB2 superconducting compounds involving 0%, 0.5%, 1.0%, 1.5% and 2% Mn content. The superconducting transition has been found to be very sharp for the pure compound of MgB2 and it is observed that the transition width increases with Mn content. For small values of Mn content, the thermo-power S(T) increases with Mn content which suggests that the hole density increases. However, with further increase in Mn content, a small decrease in S(T) is observed. For all the compounds, we have observed the expected linear region at low temperatures. There is no systematic trend in the slopes dS/dT with Mn content.Journal of Physics Conference Series 07/2010; 234(1):012033. -
Article: Electrical and thermal properties of bulk superconductors Eu0.95Pr0.05Ba2(Cu1−xMx)3O7−δ (M = Fe, Ni, Zn and Mn)
Physica C: Superconductivity. 02/2010; 470:244-249. -
Article: Electrical and thermal properties of bulk superconductors Eu0.95Pr0.05Ba2(Cu1-xMx)(3)O7-delta (M = Fe, Ni, Zn and Mn)
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ABSTRACT: Measurements of transition temperature, magneto-resistance, thermal conductivity, thermo-electric power and specific heat have been carried out on co-doped samples of Eu0.95Pr0.05Ba2(Cu1-xMx)(3)O7-delta (M = Fe, Ni, Zn and Mn) compounds It is found that all samples exhibit metallic behavior, except the co-doped sample of Fe that shows semiconducting behavior It is seen that the upper-critical field Ho decreases with Pr-doping However, an increase in H-c2 for dopants like Fe and Mn is observed Thermal conductivity for the pristine sample of EuBa2Cu3O7-delta (Eu-123) exhibits a pronounced hump below the superconducting transition temperature T-c However, the peak height of the hump decreases with Pr-doping and such a feature is further suppressed in the co-doped samples The negative sign of the measured thermo-electric power of Eu-123 indicates that the dominant carrier in this sample is electron-like, whereas it turns to hole-like for all of the doped samples A Jump in specific heat C-p is detected in the pure sample of Eu-123 at T-c, while only a change in slope in C-p is seen around the transition temperature in the Pr-doped sample. (C) 2010 Elsevier B V All rights reservedPhysica C-Superconductivity and Its Applications. 01/2010; 470(3):244-249. -
Article: Anomalous thermoelectric power of overdoped Bi2Sr2CaCu2O8 superconductor
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ABSTRACT: All the samples possess single-phase character and their superconducting transition temperatures (T<sub>c</sub><sup>R=0</sup>) are 85, 90, and 72 K, respectively for Bi2212-MQ, Bi2212- N <sub>2</sub> , and Bi2212- O <sub>2</sub> . Though the Bi2212-MQ and Bi2212- N <sub>2</sub> samples are in near optimum doping regime, the Bi2212- O <sub>2</sub> is an overdoped sample. T<sub>c</sub><sup>S=0</sup> values obtained through S(T) data are also in line with those determined from the temperature dependence of resistance (T<sub>c</sub><sup>R=0</sup>) and dc magnetization (T<sub>c</sub><sup> dia </sup>) . Interestingly, S(T) behavior of the optimally doped Bi2212-MQ and Bi2212- N <sub>2</sub> samples is seen to be positive in whole temperature range, the same is found negative for the overdoped Bi2212- O <sub>2</sub> sample above T<sub>c</sub><sup>S=0</sup> . This anomalous S(T) behavior is seen in the light of the recent band structure calculations and the ensuing split Fermi surface as determined by angle-resolved photoelectron spectroscopy.Journal of Applied Physics 12/2009; · 2.17 Impact Factor -
Article: Anomalous Thermoelectric power of over-doped Bi2Sr2CaCu2O8 superconductor
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ABSTRACT: Temperature dependence of thermoelectric power S(T) of three differently processed Bi2Sr2CaCu2O8 (Bi2212) samples, viz. as-processed melt quenched (Bi2212-MQ), 6000C N2-annealed (Bi2212-N2) and 6000C O2-annealed (Bi2212-O2) is reported here. All the samples possess single-phase character and their superconducting transition temperatures (TcR=0) are 85 K, 90 K and 72 K respectively for Bi2212-MQ, Bi2212-N2 and Bi2212-O2. While Bi2212-MQ and Bi2212-N2 samples are in near optimum doping regime, Bi2212-O2 is an over-doped sample. TcS=0 values obtained through S(T) data are also in line with those deduced from the temperature dependence of resistance and DC magnetization. Interestingly, S(T) behaviour of the optimally-doped Bi2212-MQ and Bi2212-N2 samples is seen to be positive in whole temperature range, it is found negative for the over-doped Bi2212-O2 sample above TcS=0. These results have been seen in the light of the recent band structure calculations and the ensuing split Fermi surface as determined by angle-resolved photoelectron spectroscopy (ARPES).02/2009; -
Article: Resistivity and thermopower measurement setups in the temperature range of 5-325 K.
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ABSTRACT: Automated precision measurement setups for electrical resistivity of eight metallic samples simultaneously and thermoelectric power of different types of samples in the temperature range of 5-325 K have been developed. The details of the setups and their capabilities have been described. Usually each run takes nearly 5 h and typical error is within 3% and 4%, respectively. The results of high purity Nb and Pt samples are used as examples to demonstrate this.The Review of scientific instruments 01/2009; 79(12):125103. · 1.52 Impact Factor -
Article: Size-dependent thermopower in nanocrystalline nickel
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ABSTRACT: Thermopower (S-n) of compacted nanocrystalline Ni of average particle size D=38, 32, and 25 nm at low temperatures (5-300 K) is reported here. S-n exhibits striking deviations from bulk thermopower S-bulk behavior revealing evolution of S-n with change in D. As D decreases, there is significant decrease in S-n, gradual disappearance of phonon drag minimum and sign change to positive below 38 K compared to usual negative S-bulk. They have been attributed to electron and phonon scattering at grain boundaries and phonon confinement. Small minima observed near 25 K in thermopower difference Delta S are correlated with superparamagnetic transitions. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3167302]Applied Physics Letters. 01/2009; 95(1). -
Article: Resistivity and thermopower measurement setups in the temperature range of 5–325 K
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ABSTRACT: Automated precision measurement setups for electrical resistivity of eight metallic samples simultaneously and thermoelectric power of different types of samples in the temperature range of 5–325 K have been developed. The details of the setups and their capabilities have been described. Usually each run takes nearly 5 h and typical error is within 3% and 4%, respectively. The results of high purity Nb and Pt samples are used as examples to demonstrate this.Review of Scientific Instruments 01/2009; · 1.37 Impact Factor -
Article: Grain size effect on lattice of ni nanocrystals prepared through polyol method.
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ABSTRACT: Nanocrystalline nickel powders were prepared with grain size 'd' in the range 40-100 nm diameters through polyol method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used for characterization. XRD of the prepared samples consistently matched with standard fcc structure of nickel without any impurity peak. Detailed analysis and calculations using Scherrer equation for (111) peak revealed systematic increase in line width and peak shifting towards lower diffraction 2theta angles with decrease in nickel to ethylene glycol mole ratio. Different values of d estimated from various peaks of each sample suggested associated microstrains in the nanograins. Values of d estimated from X-ray diffraction patterns were compared with those obtained from atomic force microscopy and scanning electron microscopy results, and discussed. Observed lattice expansion is explained, on the basis of a theoretical model of linear elasticity.Journal of Nanoscience and Nanotechnology 09/2008; 8(8):4127-31. · 1.56 Impact Factor -
Article: Thickness dependent structural, electronic, and optical properties of Ge nanostructures.
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ABSTRACT: In the present paper, we have investigated structural, optical as well as electronic properties of electron beam evaporated Ge thin films having layer thicknesses ranging from ultra-thin (5 nm) to thick (200 nm). The Raman spectra show that all peaks are shifted towards lower wave number as compared to their bulk counterparts and are considered as a signature of nanostructure formation and quantum confinement effect. The Raman line exhibits transformation from nanocrystalline to microcrystalline phase with a reduction in blue shift of peak position with increase in Ge film thickness (>5 nm). Similarly, the optical absorption spectra corresponding to these films also show reduction in blue shift effect, although Ge 5 nm film shows the absorption behaviour quite different from higher thickness films. The corresponding band gap values obtained from absorption measurements are much larger than bulk Ge and are mainly attributed to the effect of quantum confinement as expected for small size particles calculated from GIXRD patterns. AFM data in each case are correlated and discussed with structural as well as optical results to support the effect of growth morphology on the above-mentioned observations. The results are further supported by photoelectron spectroscopy (PES), photoluminescence (PL) and resistivity measurements and are interpreted in terms of crystallinity and quantum confinement effect.Journal of Nanoscience and Nanotechnology 07/2008; 8(6):2955-63. · 1.56 Impact Factor -
Article: Anomalous electrical transport behavior in nanocrystalline nickel.
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ABSTRACT: We have prepared nanocrystalline Ni (n-Ni) samples of grain sizes 40-100 nm using a polyol method and investigated the electrical transport on their compacted pellets in the temperature range 3-300 K. The resistivity, ρ, decreases nearly linearly with increase in compaction pressure but without a change in its slope, dρ/dT. ρ is anomalously large, and is strongly temperature and grain-size dependent. The resistivity at room temperature, ρ(300 K), is in the range ∼40-759 µΩ cm but with a positive coefficient of resistivity α (metallic). This is associated with the significantly enhanced dρ/dT with increase in residual resistivity ρ(0). These characteristics are attributed to the disorder in the grain boundaries that represents effectively a series resistor network.Nanotechnology 05/2008; 19(18):185711. · 3.98 Impact Factor -
Article: Investigations of the electrical properties in CuInSe2 and the related ordered vacancy compounds
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ABSTRACT: The conductivity mechanisms in polycrystalline CuInSe2 and the ordered vacancy compounds CuIn3Se5, CuIn5Se8 and CuIn7Se12 were studied by low temperature conductivity measurements and room temperature Hall and photoconductivity measurements. The polycrystalline films were structurally, morphologically and compositionally characterized using x-ray diffraction, atomic force microscopy and energy dispersive analysis by x-rays, respectively. In general, the films showed Mott's variable range hopping conduction in the temperature range below 200 K while above 200 K thermally activated conductivity due to grain boundary effects and defect levels was observed. To investigate the reason for the metallic behaviour shown by Cu-rich films, the films were etched and the change in behaviour was studied.Semiconductor Science and Technology 05/2004; 19(7):798. · 1.72 Impact Factor -
Article: Effect of oxygen stoichiometry variation on Tc in Nd1.85Ce0.15CuO4- delta
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ABSTRACT: The oxygen vacancy parameter, delta , in electron-doped superconducting Nd1.85Ce0.15CuO4- delta , has been varied by changing the sample-processing conditions. A Tc-onset value of 19 K was obtained by quenching alone. Tc onset as high as 24 K, Tc(R=0)=17 K and Delta T(90%-10%)=3 K have been achieved for delta =0.05 in argon-annealed single-phase Nd1.85Ce0.15CuO4- delta samples.Superconductor Science and Technology 12/1998; 5(9):561. · 2.66 Impact Factor -
Article: Ammoximation of cyclohexanone over nanoporous TS-1 using UHP as an oxidant
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ABSTRACT: Ammoximation of cyclohexanone to cyclohexanone oxime has been carried out using ammonia and urea hydrogen peroxide adducts as the oximation reagents. Effect of catalyst concentration, temperature, and molar ratio of reactants and effect of doping TS-1 with Fe has been studied to obtain the optimum conversion of cyclohexanone (CH) and selectivity to cyclohexanone oxime. The catalyst has been characterized employing the techniques of XRD, FT-IR, EDAX, SEM, AAS and Mössbauer spectroscopy with a view to confirm phase purity, stoichiometry, particle size distribution and oxidation state of Fe. The BET surface area of TS-1 catalyst was found to be 680 m2/g. A maximum conversion of about 70% of cyclohexanone with cyclohexanone oxime selectivity of 99.72% was obtained over TS-1 doped with Fe at a temperature of 40 °C and cyclohexanone to UHP molar ratio of 1:1. Reaction seems to proceed through a redox mechanism and follow hydroxylamine as well as imine routes. According to hydroxylamine route ammonia and UHP react within the TS-1 pores and produce hydroxylamine. The hydroxylamine thus formed reacts with cyclohexanone outside the pores to produce cyclohexanone oxime. In the imine route cyclohexanone and ammonia react to produce cyclohexanone imine, which is oxidized to cyclohexanone oxime. A tentative mechanism for the process has been proposed.Chemical Engineering Journal.
Top co-authors
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Institutions
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2009–2010
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UGC-DAE Consortium for Scientific Research
Indore, State of Madhya Pradesh, India -
National Physical Laboratory - India
Delhi, NCT, India
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1998
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Indian Institute of Technology Bombay
Mumbai, State of Maharashtra, India
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