193 research outputs found
Effect of high voltage on the structure and electrochemistry of LiNi0.5Mn0.5O2: A joint experimental and theoretical study
No full textA combination of neutron diffraction (ND), Li-6 magic-angle spinning NMR, electrochemistry, and first principles calculations have been used to determine and rationalize the structural changes that occur during cycling of the layered material Lix(Ni0.5Mn0.5)O-2 (x = 1), synthesized via the hydroxide route. ND and 6Li NMR experiments confirm that Li is lost from the transition metal (TM) layers, very early on in the charge process. On charging to higher voltages (above 4.5 V), the Li is lost from the tetrahedral and residual Li octahedral sites in the Li layers. This process is accompanied by a migration of more than 75% of the Ni ions originally present in the Li layers into the TM layers, to occupy the sites vacated by Li. Calculations suggest that (i) these Ni migrations occur via the tetrahedral sites, (ii) activation energies for migration depend strongly on the original position of the Ni ions in the Li layers though the driving force for migration is large (> 1 eV), and (iii) because neither Ni3+ nor Ni4+ is stable in the tetrahedral site, migration will not occur once the Ni ions in the Li layers are oxidized to Ni3+ or Ni4+. Electrochemical measurements (open circuit voltage, OCV, and galvanostatic mode) are consistent with a high voltage process (approximately 4.6 V) associated with a large activation energy. The new Ni sites in the TM layers are not necessarily stable, and on discharge, 60% of the ions return to the Li layers. In particular, Ni ions surrounded by six Mn4+ ions are found (in the calculations) to be the least stable. Because the Li ions originally in the TM layers in the as-synthesized sample are predominantly in this environment, this is consistent with the Ni migration observed experimentally. Materials charged to 5.3 V can be cycled reversibly with stable capacities of over 180 mAh g(-1).The work was supported by the Assistant
Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. DOE
under Contract No. DE-AC03-76SF00098, via subcontracts No.6517748 and 6517749 with the Lawrence Berkeley National Laboratory. We would also like to acknowledge the support
form the Center for Materials Science and Engineering, MIT, and the MRSEC program of the NSF under award number DMR 02-13282. Y.S.-H. acknowledges the Office of Naval Research Young Investigator Award No. N00014-03-10448 for financial support. The ISIS Facility of the Rutherford Appleton Labora-tory is thanked for access to GEM. This work has benefited from the use of NPDF at the Lujan Center at the Los Alamos Neutron Science Center, funded by the DOE Office of Basic Energy Sciences (BES), Los Alamos National Laboratory, and the DOE under Contract No. W-7405-ENG-36. The upgrade
of NPDF has been funded by NSF through Grant DMR 00-76488. This work has benefited from the use of the Intense Pulsed Neutron Source at Argonne National Laboratory. This
facility is funded by the U.S. DOE under Contract No. W-31-109-ENG-38. Use of the NSLS, Brookhaven National Laboratory,
was supported by the U.S. DOE, Office of BES, under Contract No. DE-AC02-98CH10886. We are grateful for the assistance given to us at the different beam lines from Thomas
Proffen (NPDF, LANL), Winfried Kockelmann (GEM, ISIS),Yongjae Lee (X7A, NSLS), James Richardson, Evan Maxey, and Ashfia Huq (GPPD, IPNS). We thank Jordi Cabana for
electrochemical measurements as well as Matthias Gutmann and Alan Soper for their help in neutron data analysis
Thecamoebian fossil record of the families Arcellidae and Centropyxidae Thecamoebians preserved in sediments noted by a circle, whereas thecamoebians preserved in amber are noted by a triangle.
No full text<p>The basal part of the figure depicting ecology of the genera <i>Centropyxis</i> and <i>Arcella</i> through time has been modified in the light of this study and other published data. (a) Wolf, 1995; (b) Kumar et al., 2011; (c) Farooqui et al., 2014; (d) Wightmann et al., 1994; (e) Medioli et al., 1990a; (f) Schönborn et al., 1999; (g) Poinar et al., 1993; (h) Schmidt et al., 2004;(i) Waggoner, 1996b; (j) van Hengstum et al., 2007; (k) Porter and Knoll, 2000 and (*) denotes this study. The geological time axis is not to scale. The figure has been modified after van Hengstum et al. 2007 (with written permission from the original author van Hengstum).</p
Infrared and Raman spectroscopic studies of glasses with NASICON - type chemistry
No full textStructures of NASICON glasses of the general formula AB2(PO4)3, where A = Li, Na or K and B = Fe, Ga, Ti, V or Nb, have been investigated using vibrational (IR and Raman) spectroscopies. Phosphate species appear to establish an equilibrium via a disproportionation reaction involving a dynamical bond-switching mechanism where both charge and bonds are conserved. B ions in the system acquire different coordinations to oxygens. Alkali ions cause absorptions due to cage vibrations. All the observed spectroscopic features are consistent with speciation involving disproportionation reactions
Infrared and Raman spectroscopic studies of glasses with NASICON - type chemistry
No full textStructures of NASICON glasses of the general formula AB2(PO4)3, where A = Li, Na or K and B = Fe, Ga, Ti, V or Nb, have been investigated using vibrational (IR and Raman) spectroscopies. Phosphate species appear to establish an equilibrium via a disproportionation reaction involving a dynamical bond-switching mechanism where both charge and bonds are conserved. B ions in the system acquire different coordinations to oxygens. Alkali ions cause absorptions due to cage vibrations. All the observed spectroscopic features are consistent with speciation involving disproportionation reactions
South Asian Figurines in the British Museum: Literature Review and Analysis
No full textIn the early twenthieth century in British India, many military officers were also amateur archaeologists. Some of them, including Colonel D.H. Gordon and Colonel D.R. Martin, collected human terracotta figurines. The figurines in this collection came from the northwest of pre-partition India, mostly from villages in the vicinity of Peshawar in Pakistan. They were bought from farmers or antiquities dealers. Thus this is a surface collection. The figurines were then sold or donated to the British Museum. There they were stored without being studied.
This purpose of this thesis is two-fold: 1) to review the literature on South Asian human figurines, and 2) to analyze and interpret a collection of figurines that has not so far been published. The analysis includes a description of the characteristics of the figurines, and interpretations of their functions and meanings. There are four major types of figurines, based on decorations and facial features: Sar Dheri, Sahri Bahlol, Hellenistic and “other”. The Sar Dheri figurines with rosettes may represent an unknown folk deity as the decorations are not the symbol of any deity that appears in Hindu, Jain or Buddhist mythology. The Sahri Bahlol figurines greatly resemble those figurines identified as Naigameśīs in other excavation reports. The analysis ends by proposing further research in South Asian terracotta figurines that would lead to a detailed history of the evolution of figurines in South Asia from Mehrgarh to the present
Estimation of population using LnP(D) derived Δk for k from 1 to20, (a) SSRs and (b) SNPs.
No full text<p>Estimation of population using LnP(D) derived Δk for k from 1 to20, (a) SSRs and (b) SNPs.</p
Multialkali phosphate glasses: a new window to understand the mechanism of ion transport
No full textAlkali metaphosphate glasses containing two and three alkalis have been prepared by melt-quenching method over a wide range of compositions. Several properties of these glasses such as density, molar volume, glass transition temperature, heat capacity jump and NMR chemical shift of 31P, 23Na and 7Li nuclei have been measured. Transport properties have been studied over a wide range of frequency and temperature. Mixed alkali effect (MAE), which manifests in three alkali containing glasses is found to be complex. Arrhenius plots of d.c. conductivities are characterized by two slopes and a.c. conductivities display two power-law regimes with two characteristic s values. The imaginary part of the electric modulus exhibits a unique two peak relaxation behaviour and the peaks merge at higher temperatures. This is first time such a behaviour has been observed in a.c. conductivity and dielectric relaxation of glasses. A new mechanism has been proposed to understand ion transport in oxide glasses, which rationalizes all the observations made in the trialkali phosphate system examined here
Dielectric relaxation in glasses: possible origin of the stretched relaxation behaviour
No full textThe origin of non-Debye dielectric relaxation observed widely in network forming glasses is examined. It is attributed to the presence of two polarization centers, which relax in the manner of Debye polarization with a time delay between them. The experimentally observed relaxation therefore appears broadened and is fitted well by the powerful Kohlrausch-Williams-Watts (KWW) stretched relaxation function. It is shown that the relaxation behaviour predicted by the present model is in very good agreement with both the experimental and KWW generated relaxation behaviour
Model based clustering of (a) SSR (K=5) and (b) SNP (K=15) of Indica rice cultivars, (boxes indicates distribution of Autumn rice, also known as 'Aus' in West Bengal, 'Ahu' in Assam, 'Beali' in Orissa, 'Bhadai' in Bihar, 'Virippu' in Kerala and 'Kuruvai/kar/ Sornavari' in Tamil Nadu).
No full text<p>Model based clustering of (a) SSR (K=5) and (b) SNP (K=15) of Indica rice cultivars, (boxes indicates distribution of Autumn rice, also known as 'Aus' in West Bengal, 'Ahu' in Assam, 'Beali' in Orissa, 'Bhadai' in Bihar, 'Virippu' in Kerala and 'Kuruvai/kar/ Sornavari' in Tamil Nadu).</p
Multialkali phosphate glasses: a new window to understand the mechanism of ion transport
No full textAlkali metaphosphate glasses containing two and three alkalis have been prepared by melt-quenching method over a wide range of compositions. Several properties of these glasses such as density, molar volume, glass transition temperature, heat capacity jump and NMR chemical shift of 31P, 23Na and 7Li nuclei have been measured. Transport properties have been studied over a wide range of frequency and temperature. Mixed alkali effect (MAE), which manifests in three alkali containing glasses is found to be complex. Arrhenius plots of d.c. conductivities are characterized by two slopes and a.c. conductivities display two power-law regimes with two characteristic s values. The imaginary part of the electric modulus exhibits a unique two peak relaxation behaviour and the peaks merge at higher temperatures. This is first time such a behaviour has been observed in a.c. conductivity and dielectric relaxation of glasses. A new mechanism has been proposed to understand ion transport in oxide glasses, which rationalizes all the observations made in the trialkali phosphate system examined here
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