Gargi College

Delhi, India

Gargi College

Delhi, India
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Archana,Gargi College | Gupta H.C.,Indian Institute of Technology Delhi
AIP Conference Proceedings | Year: 2016

Raman and infrared investigations of the recent Aurivillius oxides K0.25Na0.25La0.5Bi2Nb2O9(KNBN-La) and K0.25Na0.25Bi2.5Nb2O9(KNBN-Bi) has been made using normal coordinate analysis in orthorhombic A21am space group. The calculation of zone center phonons incorporates nine stretching and nine bending force constants. The Raman and the infrared frequencies have been assigned and calculated in a very good agreement with the observed frequencies. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wavenumbers. © 2016 Author(s).

Raghuvanshi S.,The Interdisciplinary Center | Kapoor M.,University of Delhi | Tyagi S.,Gargi College | Kapoor S.,The Interdisciplinary Center | And 3 more authors.
Molecular Breeding | Year: 2010

Rice is one of the pillars of world-wide food security. Improvement in its yield is necessary to mitigate hunger of millions of people who depend on rice as a staple. Decoding rice genome sequence is expected to complement efforts being made to improve rice and its yield. The information about more than 32,000 genes, regulatory elements, repeat DNA, and DNA markers opens-up new horizons for molecular analysis and genetic enhancement not only for rice but also for other cereal crops. In the post-genomic era, significant progress has been made on defining transcriptome and epigenome as well as gene discovery by way of forward and reverse genetic approaches. Efforts are on to fill the gap between the genome and the phenotype. This may lead to regular practice of genomics-assisted breeding of rice. © 2009 Springer Science+Business Media B.V.

Anita,Gargi College | Luthra V.,Gargi College
Ceramics International | Year: 2014

The preparation of pure ZnO, doped [(Zn0.99M0.01)O] and co-doped [(Zn0.99Al.01-xNix)O: x=.005,.007] materials, where M=Al, Ni has been carried out by co-precipitation route. The results of various characterizations such as X-ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) and dc conductivity measurements on these samples have been reported. The temperature variation of dc conductivity has been used to delineate the changes in the activation energy. A unique plot depicting the variation of activation energy with temperature has been obtained. These results show the potential of aluminium and nickel co-doped ZnO for spintronic applications. © 2014 Elsevier Ltd and Techna Group S.r.l.

Pugh D.C.,University College London | Luthra V.,Gargi College | Singh A.,Gargi College | Parkin I.P.,University College London
RSC Advances | Year: 2015

A series of indium doped ZnO (IZO) materials were fabricated, characterised and tested for their gas sensing properties. ZnO was synthesised with indium doping levels of 0.2, 0.5, 1 and 3 mol%. These were fabricated into gas sensors. Production took place using a commercially available screen printer, a 3 × 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. Materials were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Electrical conductivity of all samples was also calculated. Sensors were exposed to ethanol, methanol, n-butanol and acetone at concentrations between 5 and 80 ppm. Low levels of indium doping were found to increase the responsiveness of the sensors. However, higher levels of doping were found to inhibit conductivity and responsiveness to gases of IZO sensors. Sensors with low levels of indium doping were found to show minimal response to other gases, demonstrating a lack of cross sensitivity. These sensors show potential for inclusion into an electronic nose for with the aim of selective alcohol detection. © The Royal Society of Chemistry 2015.

Sachdeva A.,University of Delhi | Kumar M.,National Physical Laboratory India | Luthra V.,University of Delhi | Luthra V.,Gargi College | Tandon R.P.,University of Delhi
Applied Physics A: Materials Science and Processing | Year: 2011

We report here the formation of single phase lead zirconate titanate (PZT) nanopowder with composition Pb(Zr0.52Ti0.48)O3 and average crystallite size 12-20 nm, synthesized by sol-gel process. The phase evolution of PZT gel powder, heat treated at temperatures 550, 650 and 800°C was monitored by X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS). The high resolution XPS spectra of Pb4f, Zr3d, Ti2p and O1s show that PZT with pure perovskite structure is obtained at 800°C while at lower temperatures pyrochlore phase co-exists with perovskite phase. The XRD results also support this analysis. We have also identified the pyrochlore phase using XPS by analyzing the corresponding variations in the FWHM values, peak positions and the separation between the spin doublets of Pb, Zr and Ti associated with it. The composition of the final powder obtained with pure perovskite structure is calculated and is close to the designed value. © 2011 Springer-Verlag.

Sachdeva A.,University of Delhi | Gautam P.,University of Delhi | Luthra V.,University of Delhi | Luthra V.,Gargi College | Tandon R.P.,University of Delhi
Integrated Ferroelectrics | Year: 2010

Modified sol-gel method alongwith the infilteration process have been used to deposit dense, crack-free ferroelectric lead zirconate titanate (PZT) 0-3 ceramic/ceramic composite films of composition Pb(Zr0.52Ti 0.48)O3 and thickness greater than 10 μm onto a platinum coated silicon substrate. PZT powder with the same composition was dispersed using a dispersant ESL400 in PZT sol to obtain a slurry. The slurry and the sol were alternatively deposited on the substrate followed by drying, pyrolysis and final annealing at 750°C to get single phase perovskite structure of the film. Thickness of the film was determined by SEM. Surface morphology of the film was studied by AFM. Raman spectrum of the film depicts coexistence of rhombohedral and tetragonal phases. Temperature dependence of dielectric constant shows that the films exhibit diffused phase transition rather than relaxor behavior. The remanant polarization (Pr) and coercive field (Ec) of the resulting film are 13.5 μC/cm 2 and 57 kV/cm respectively. Copyright © 2010 Taylor & Francis Group, LLC.

Gupta S.K.,National Physical Laboratory India | Luthra V.,Gargi College | Singh R.,National Physical Laboratory India
Bulletin of Materials Science | Year: 2012

A detailed comparative study of electron paramagnetic resonance (EPR) in conjunction with d.c. electrical conductivity has been undertaken to know about the charge transport mechanism in polyaniline (PANI) doped with monovalent and multivalent protonic acids. This work is in continuation of our previous work for further understanding the conduction mechanism in conducting polymers. The results reveal that the polarons and bipolarons are the main charge carriers formed during doping process and these cause increase in electrical conductivity not only by increase in their concentration but also because of their enhanced mobility due to increased inter-chain transport in polyaniline at high doping levels. EPR line asymmetry having Dysonian line shape for highly doped samples shows a marked deviation of amplitudes A/B ratio from values close to one to much high values as usually observed in metals, thereby support the idea of high conductivity at higher doping levels. The nature of dopant ions and their doping levels control the charge carriers concentration as well as electrical conductivity of polyaniline. The electrical conductivity has also been studied as a function of temperature to know the thermally assisted transport process of these charge carriers at different doping levels which has been found to follow the Mott's variable range hopping (VRH) conduction model for all the three dopants used. The charge carriers show a change over from 3D VRH to quasi 1D VRH hopping process for multivalent ions at higher doping levels whereas 1D VRH has been followed by monovalent ion for full doping range. These studies collectively give evidence of inter-chain percolation at higher doping levels causing increase in effective mobility of the charge carriers which mainly seems to govern the electrical conduction behaviour in this system. © Indian Academy of Sciences.

Sachdeva A.,University of Delhi | Luthra V.,University of Delhi | Luthra V.,Gargi College | Gautam P.,University of Delhi | Tandon R.P.,University of Delhi
Integrated Ferroelectrics | Year: 2010

Bulk samples of Pb(1-x)CaxZr0.52Ti 0.48O3 (x = 0,0.02,0.04,0.06,0.08,0.1) have been synthesized by sol-gel process using lead acetate trihydrate, calcium acetate hydrate, zirconium propoxide and titanium propoxide as the starting materials. The dependence of ferroelectric phase transition temperature Tc as a function of calcium substitution has been investigated. A linear decrease of Tc is observed with increasing calcium concentration. The variation of room temperature dielectric constant and that of maximum value of dielectric constant corresponding to the phase transition temperature are explained by the microstructural studies. XRD patterns of the samples show that all the compositions sintered at 1200°C are having single phase with perovskite structure. P-E hysteresis loop measurements showed that calcium modified PZT ceramics have higher Pr values than that of pure PZT composition prepared by sol-gel method. The composition with 4 mol% calcium has the highest value of Pr, 25.2 μC/cm2 and lowest Ec, 9.6 kV/cm. Copyright © 2010 Taylor & Francis Group, LLC.

Jain R.,University of Delhi | Luthra V.,Gargi College | Gokhale S.,University of Delhi
Journal of Magnetism and Magnetic Materials | Year: 2016

The effect of dysprosium doping on evolution of structural and magnetic properties of magnetite (Fe3O4) nanoparticles is reported. A standard route of co-precipitation was used for the synthesis of undoped and doped magnetite nanoparticles Fe3-xDyxO4 (x=0.0-0.1). Transmission electron microscopy (TEM) shows formation of round shaped particles with diameter in the range of 8-14 nm for undoped sample. On doping beyond x=0.01, the formation of rod like structures is initiated along with the round shaped particles. The number of rods is found to increase with increasing doping concentration. Magnetic characterization using Vibrating Sample Magnetometer (VSM) revealed doping dependent magnetic properties which can be correlated with the crystallite size as determined from X-ray diffraction (XRD). Enhancement in the saturation magnetization in the initial stages of doping can be explained on the basis of incorporation of Dy3+ ions in the inverse spinel structure at the octahedral site in place of Fe3+ ions. Subsequent decrease in saturation magnetization observed beyond x=0.03 could be attributed to precipitation of excess Dy in form of dysprosium ferrite phase. © 2016 Elsevier B.V. All rights reserved.

Luthra V.,Gargi College | Singh A.,Gargi College | Pugh D.C.,University College London | Parkin I.P.,University College London
Physica Status Solidi (A) Applications and Materials Science | Year: 2016

This paper presents a comparative study on gas sensing properties of pure and doped ZnO nano powders. To facilitate doping, Aluminum and nickel precursors were used as dopant/co-dopants using a simple and reproducible co-precipitation method. Pure ZnO and samples with compositions Zn0.99M0.01O (M = Al/Ni) and Zn0.99Al0.005Ni0.005O were prepared to evaluate the effect of Al/Ni doping/co-doping. The samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM). The electrical conductivity of these samples was measured. A temperature variation of electrical conductivity was used to calculate activation energy of various samples. The samples were subjected to ethanol tests at concentration ranging between 10 and 50 ppm. The metal ion doping showed a marked increase in relative responsiveness of all doped samples. The variation in gas sensing response has been correlated with electrical conductivity, activation energy, and morphology of these samples. This report clearly demonstrates inter-connection of multiple factors influencing gas sensing properties of metal oxide semiconductors (MOS). Similar tests performed with methanol exposure show much reduced relative responses for all the samples in comparison to ethanol. These studies can be exploited for tailoring of futuristic sensors with improved responses. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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