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Tirupati, India

Nallamuthu N.,Pondicherry University | Prakash I.,Pondicherry University | Satyanarayana N.,Pondicherry University | Venkateswarlu M.,Amara Raja Batteries Ltd.
Journal of Alloys and Compounds

Nanocrystalline apatite type structured lanthanum silicate (La 10Si6O27) sample was synthesized by sol-gel process. Thermal behavior of the dried gel of lanthanum silicate sample was studied using TG/DTA. The structural coordination of the dried gel of lanthanum silicate, calcined at various temperatures, was identified from the observed FTIR spectral results. The observed XRD patterns of the calcined dried gel were compared with the ICDD data and confirmed the formation of crystalline lanthanum silicate phase. The average crystalline size of La10Si 6O27 was calculated using the Scherrer formula and it is found to be ∼80 nm. The observed SEM images of the lanthanum silicate indicate the formation of the spherical particles and the existence of O, Si and La in the lanthanum silicate are confirmed from the SEM-EDX spectrum. The grain and grain boundary conductivities are evaluated by analyzing the measured impedance data, using winfit software, obtained at different temperatures, of La10Si6O27 sample. Also, the observed grain and grain boundary conductivity behaviors of the La10Si 6O27 sample are analysed using brick layer model. The electrical permittivity and electrical modulus were calculated from the measured impedance data and were analyzed by fitting through the Havriliak and Negami function to describe the dielectric relaxation behavior of the nanocrystalline lanthanum silicate. © 2010 Elsevier B.V. All rights reserved. Source

Padmaraj O.,Pondicherry University | Nageswara Rao B.,Pondicherry University | Jena P.,Pondicherry University | Venkateswarlu M.,Amara Raja Batteries Ltd. | Satyanarayana N.,Pondicherry University
Polymer (United Kingdom)

Poly(vinylidene fluoride-co-hexafluoropropylene) P(VdF-co-HFP)/magnesium aluminate (MgAl2O4) hybrid fibrous nanocomposite polymer electrolyte membranes were newly prepared by electrospinning method. The as-prepared electrospun pure and nanocomposite fibrous polymer membranes with various MgAl2O4 filler contents were characterized by X ray diffraction, differential scanning calorimetry and scanning electron microscopy techniques. The fibrous nanocomposite polymer electrolytes were prepared by soaking the electrospun membranes in 1 M LiPF6 in EC:DEC (1:1, v/v). The fibrous nanocomposite polymer electrolyte membrane with 5 wt.% of MgAl2O4 show high electrolyte uptake, enhanced ionic conductivity is found to be 2.80 × 10-3 S cm-1 at room temperature and good electrochemical stability window higher than 4.5 V. Electrochemical performance of commercial celgard 2320, fibrous pure and nanocomposite polymer electrolyte (PE, NCPE) membranes with different MgAl 2O4 filler content is evaluated in Li/celgard 2320, PE, NCPE/LiCoO2 CR 2032 coin cells at current density 0.1 C-rate. The NCPE with 5 wt.% of MgAl2O4 delivers an initial discharge capacity of 158 mAhg-1 and stable cycle performance compared with the other cells containing celgard 2320 separator and pure membrane. © 2013 Elsevier Ltd. All rights reserved. Source

Nageswara Rao B.,Pondicherry University | Muralidharan P.,Pondicherry Engineering College | Ramesh Kumar P.,Pondicherry University | Venkateswarlu M.,Amara Raja Batteries Ltd. | Satyanarayana N.,Pondicherry University
International Journal of Electrochemical Science

A rapid and efficient two-steps growth strategy has been adopted to synthesize monodisperse single-crystalline spinel LiMn2O4 nanorods. The first step is to synthesize crystalline β-MnO2 nanorods through rapid microwave hydrothermal process followed by second step as solid state reaction between β-MnO2 nanorods and LiOH.H2O to obtain pure spinel LiMn2O4 nanorods. In addition, the possible formation mechanism of the β-MnO2 and spinel LiMn2O4 nanorods was also discussed. The spinel LiMn2O4 nanorods have an average diameter of 190 nm and length of 0.8-1.3 μm. Galvanostatic battery testing shows that the spinel LiMn2O4 nanorods have delivered a stable charge and discharge capacities of 98 and 96 mAhg-1, respectively, after 50 cycles at 0.1C rate in the voltage range 3.1-4.4 V. The cathode material exhibits good electrochemical performance even at high C-rates. The developed LiMn2O4 nanorods show a higher coulombic efficiency and also good rate capability attributed to the formation of the single-crystalline spinel LiMn2O4 with nanorod morphology. © 2014 by ESG. Source

Padmaraj O.,Pondicherry University | Venkateswarlu M.,Amara Raja Batteries Ltd. | Satyanarayana N.,Pondicherry University
Ceramics International

Nanocrystalline spinel type magnesium aluminate (MgAl2O4) ceramic material was synthesized by gel-combustion method. The structural, microstructural, morphology, electrical and dielectric properties of the prepared spinel type MgAl2O4 ceramic material were studied by different techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), surface area analyzer (BET) and impedance spectroscopy. The X-ray diffraction pattern and IR spectrum of magnesium aluminate material confirm the formation of impurity free nanocrystalline phase with spinel structure. The specific surface area calculated from the 1/[W((Po/P)-1)] vs relative pressure (P/Po) plot of the annealed MgAl2O4 powder is found to be 162.704 m2/g. The temperature dependent conductivity of nanocrystalline MgAl2O4 pellet was studied and the conductivity of nanocrystalline MgAl2O4 pellet at 573 K is found to be 4.9213×10-13 S cm-1. The activation energies were evaluated from log σT vs 1000/T plot of the observed two different temperature dependent conductivity regions of the nanocrystalline MgAl2O4 sample and are found to be E1=0.1828 eV (<503 K) and E2=0.8791 eV (>503 K). © 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Source

Nallamuthu N.,Pondicherry University | Prakash I.,Pondicherry University | Satyanarayana N.,Pondicherry University | Venkateswarlu M.,Amara Raja Batteries Ltd.
Materials Research Bulletin

Different compositions of scheelite type nanocrystalline La doped BaMoO4 [Ba1-xLaxMoO4+x/2, where x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5] samples were prepared by acrylamide assisted sol-gel combustion process. Dried gels prepared at 60 °C were heated at different temperatures and characterized using TG/DTA, XRD, FTIR and SEM-EDX techniques. From XRD patterns, crystalline phases for La doped BaMoO4 samples were confirmed and their average crystallite sizes were calculated using Scherrer's formula and it was found to be less than 80 nm. Structure and thermal behavior of scheelite type nanocrystalline La doped BaMoO4 samples were identified respectively using FTIR and TG/DTA measurements. Microstructure and existence of O, La, Ba and Mo elements in the La doped BaMoO4 samples were obtained from SEM-EDX and HRTEMtechniques. The 'd' spacing values were obtained for different (h k l) planes and were well matched with the standard BaMoO4. (h k l) values for different directions of planes were assigned for the observed HRTEM images and were matched with standard BaMoO4. Grain and grain boundary conductivities were evaluated by analyzing the impedance data, using the Winfit software, measured at different temperatures. © 2010 Elsevier Ltd. All rights reserved. Source

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