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PublicationConference Paper Functionalization effects on the electrical properties of Multi-walled carbon nanotube-polyacrylamide composites(2009) Seema Awasthi; Kalpana Awasthi; Rajesh Kumar; O.N. SrivastavaMulti-walled carbon nanotubes (MWNTs)-polyacrylamide (RAM) composites have been prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It has been shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. As the MWNTs loading increases from 0 to 40 wt% electrical conductivity of composite film increases by ∼7 orders of magnitude whereas the electrical conductivity of functionalized composite film increases only ∼4 orders of magnitude with respect to the pure RAM film. A model based on power law percolation for the electronic behavior of above composite has been developed and shows good agreement with the experimental data. Copyright © 2009 American Scientific Publishers.PublicationArticle Spray pyrolysis deposited multiferroic BiFeO3 films(2009) P.K. Siwach; Jai Singh; H.K. Singh; G.D. Varma; O.N. SrivastavaBiFeO3 (BFO) films were prepared by nebulized spray pyrolysis technique on a single crystal LaAlO3 (001) substrate at ∼300 °C and annealing in oxygen at ∼550 °C for 1 h. In all films BFO is the majority phase having a rhombohedrally distorted structure with R3m symmetry and lattice parameters are a=3.96 Å and α=89.7°. Atomic force microscopy reveals smooth and dense surface morphology. Despite the G -type antiferromagnetic spin structure of BFO the present BFO show well-defined M-H loops and unexpected ferromagnetism as evidenced by large saturation magnetization, ∼125 emu/cc. The origin of anomalous ferromagnetism in the present films has been traced to the presence of nanometric Fe2 O3 embedded in the BFO matrix. © 2009 American Institute of Physics.PublicationArticle Hydrogen energy in changing environmental scenario: Indian context(2009) M. Sterlin Leo Hudson; P.K. Dubey; D. Pukazhselvan; Sunil Kumar Pandey; Rajesh Kumar Singh; Himanshu Raghubanshi; Rohit. R. Shahi; O.N. SrivastavaThis paper deals with how the Hydrogen Energy may play a crucial role in taking care of the environmental scenario/climate change. The R&D efforts, at the Hydrogen Energy Center, Banaras Hindu University have been described and discussed to elucidate that hydrogen is the best option for taking care of the environmental/climate changes. All three important ingredients for hydrogen economy, i.e., production, storage and application of hydrogen have been dealt with. As regards hydrogen production, solar routes consisting of photoelectrochemical electrolysis of water have been described and discussed. Nanostructured TiO2 films used as photoanodes have been synthesized through hydrolysis of Ti[OCH(CH3)2]4. Modular designs of TiO2 photoelectrode-based PEC cells have been fabricated to get high hydrogen production rate (∼10.35 lh-1 m-2). However, hydrogen storage is a key issue in the success and realization of hydrogen technology and economy. Metal hydrides are the promising candidates due to their safety advantage with high volume efficient storage capacity for on-board applications. As regards storage, we have discussed the storage of hydrogen in intermetallics as well as lightweight complex hydride systems. For intermetallic systems, we have dealt with material tailoring of LaNi5 through Fe substitution. The La(Nil - xFex)5 (x = 0.16) has been found to yield a high storage capacity of ∼2.40 wt%. We have also discussed how CNT admixing helps to improve the hydrogen desorption rate of NaAlH4. CNT (8 mol%) admixed NaAlH4 is found to be optimum for faster desorption (∼3.3 wt% H2 within 2 h). From an applications point of view, we have focused on the use of hydrogen (stored in intermetallic La-Ni-Fe system) as fuel for Internal Combustion (IC) engine-based vehicular transport, particularly two and three-wheelers. It is shown that hydrogen used as a fuel is the most effective alternative fuel for circumventing climate change. © 2009 International Association for Hydrogen Energy.PublicationConference Paper On the synthesis and characterizations of TiO 2 nanotubes(2009) P.K. Dubey; P.R. Mishra; A.S.K. Sinha; O.N. SrivastavaIn the present work, aligned TiO 2 nanotubes have been synthesized by a simple method of electrochemical anodization of high purity, well cleaned, etched and ultrasonicated Ti-sheet (Purity ∼99.99%) in a fluoride mediated electrolytic media consisting of a solution of 0.14 M NaF and a solution of 0.5 M/1.0 M H 3PO 4. Studies on the effects of anodization voltage, time and electrolyte concentration on the formation of TiO 2 nanotubes have been carried out. The TiO 2 nanotube arrays have been synthesized at applied anodization voltages of ∼10 V and ∼20 V. The anodization was carried out for 1 hour and 2 hours at each applied voltage. Structural/microstructural characterizations of TiO 2 nanotubes have been carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of TiO 2 nanotubes showed interesting features relating to morphology, the pore size (diameter of the tubes) and the lengths of the tube. TEM investigations revealed that the as synthesized nanotubes are amorphous in nature and on electron beam annealing, these transformed to crystalline phases (rutile and brookite). The optical characterizations through UV-Visible spectroscopy exhibited that the band gap are ∼3.03 eV and ∼2.87 eV for tubes synthesized at applied anodization voltages of ∼10 V and ∼20 V respectively. A tentative mechanism for the growth of TiO 2 nanotube has been put forward. Copyright © 2009 American Scientific Publishers All rights reserved.PublicationArticle Effect of annealing below crystallization temperature on structural and mechanical properties of Co66Si16B12Fe 4Mo2 metallic glass(National Institute of Optoelectronics, 2009) P. Kumar; K. Singh; T.P. Yadav; O.N. SrivastavaThe influence of thermal treatment on the structural and mechanical properties of Co66Si16B12Fe4Mo 2 metallic glass has been investigated in present study. Co 66Si16B12Fe4Mo2 metallic glass has been subjected to isothermal annealing at 450°C for different time such as 1, 2, 5 and 8 h and studied by X-ray diffraction and scanning electron microscopy techniques. The Voight function analysis has been used for calculation of effective crystallite size and relative strain of all the annealed samples. The crystallite size has been found to be ̃ 40 - 60 nm after different h of annealing. The mechanical properties of above alloy before and after annealing has been studied by micro-hardness technique. Sample annealed for 8 h at 450°C becomes completely crystallized due to local structural rearrangements of the amorphous matrix by promoting the retention of nucleation during annealing and shows the maximum hardness among all crystalline and glassy samples.PublicationArticle Broad temperature range low field magnetoresistance in La0.7Ca0.3MnO3:nano-ZnO composites(2009) P.K. Siwach; Pankaj Srivastava; Jai Singh; H.K. Singh; O.N. SrivastavaWe report the enhanced low field magnetoresistance in broad temperature range (∼70 K) in LCMO:(%x) nano-ZnO (%x = 0, 1, 3, 5, 7 and 10) composites. Nano-ZnO has been synthesized by vapor phase transport technique which then admixed with sol-gel synthesized nano-LCMO that leads to LCMO:nano-ZnO composites. Nano-ZnO admixing does not show any significant change in lattice parameter of the composites. All samples exhibits characteristic insulator-metal (TIM) and para-ferromagnetic (TC) transition temperature, which decreases with increase in nano-ZnO content. Higher nano-ZnO (x ≥ 3%) leads to dual I-M as well as PM-FM transitions. The first transition occurs close to TIM or TC of pure LCMO and another at a significant lower temperature. At x > 7%, the double transitions transforms into a single-broad transition and at then finally disappears for x > 10%. The occurrence of dual transition has been explained on the basis of stress induced phase separation due to nanoglobular ZnO structures that result in formation of intragranular and intergranular regions having different transition temperatures. The interesting and important result for the present LCMO:nano-ZnO composites is the observation of improved MR ∼13-18% at a moderate magnetic field of 3 and 5 kG in a broad temperature range of ∼70 K (80-150 K). The improved broad range low field magnetoresistance (LFMR) has been explained on the basis of grain boundary tailoring due to coating of polar nature nano-ZnO on the LCMO grains. © 2009 Elsevier B.V. All rights reserved.PublicationArticle Synthesis and microstructural studies ofiron oxypnictide LaO 1-xFxFeAs superconductors(2009) Chandra Shekhar; Sonal Singh; P.K. Siwach; H.K. Singh; O.N. SrivastavaWe report on the synthesis and structural/microstructural studies of iron-based fluorine doped LaOFeAs superconductors. We have successfully synthesized fluorine doped superconducting LaO1-xFxFeAs materials by choosing lower temperature (∼1150 °C) and longer synthesis duration (∼60h) as compared to the standard values of these employed in the pioneering first contribution (Kamihara et al 2008 J.Am.Chem.Soc. 130 3296). A decrease of lattice parameters, as determined by x-ray diffraction, confirms the substitution of fluorine. The superconducting transition temperature is 27.5K which is observed at a doping level of x = 0.2. This superconducting material LaO1-xFxFeAs exhibits interesting microstructural characteristics. These relate to the existence of another structural phase, besides the standard phase, having c parameters of ∼12.67. This suggests the existence of a modulated structure, similar to the cuprates, in these new oxypnictides. This phase may have new impact on this new high-TC family. © 2009 IOP Publishing Ltd.PublicationArticle Effect of growth temperature on bamboo-shaped carbon-nitrogen (C-N) nanotubes synthesized using ferrocene acetonitrile precursor(2009) Ram Manohar Yadav; Pramod Singh Dobal; T. Shripathi; R.S. Katiyar; O.N. SrivastavaThis investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C-N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C-N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation.PublicationArticle Optical investigations of interaction between zinc tetra phenyl porphyrin and CdSe nanoparticles(2009) N.B. Lihitkar; S.B. Singh; Jai Singh; O.N. Srivastava; R.H. Naik; S.K. KulkarniInteractions between nanoparticles of zinc tetra phenyl porphyrin (ZnTPP) with CdSe nanoparticles in dimethyl sulphoxide solvent have been investigated. A ZnTPP-CdSe complex was formed which showed substantial changes in the UV-Vis absorption spectra in the presence of CdSe. Fluorescence measurements showed an interesting behavior at low as well as high concentrations of CdSe. When low concentrations of CdSe nanoparticles were added to the ZnTPP nanoparticles solution, besides two fluorescence bands due to ZnTPP nanoparticles, an intense new band appeared. On the other hand at high concentrations of CdSe one of the fluorescence band of ZnTPP at ∼604 nm increased. © 2009.PublicationArticle Investigations on hydrogenation behaviour of CNT admixed Mg2Ni(2009) Sunil Kumar Pandey; Rajesh Kumar Singh; O.N. SrivastavaThe aim of the present paper is to report results on hydrogenation behaviour of the new composite material Mg2Ni: CNT. Admixing of carbon nanotubes (CNT) in storage material Mg2Ni leads to noticeable enhancement in desorption kinetics as well as storage capacity. We have found that the composite material Mg2Ni-2 mole% CNT is the optimum material. The Mg2Ni-CNT composite exhibits hydrogen desorption rate of 5.7 cc/g/min as against 3.0 cc/g/min for Mg2Ni alone (enhancement of ∼ 90%) and storage capacity of ∼ 4.20 wt% in contrast to ∼3.20 wt% for Mg2Ni alone (increase of ∼ 31%). Feasible mechanisms for the enhancement of hydrogen desorption kinetics and storage capacity have been put forward. © 2009 Professor T. Nejat Veziroglu.