3,674 research outputs found
NASICON materials - a long neglected class of solid electrolytes
The so-called NASICON materials AT2P3O12 (A = alkaline metal, T = tetravalent transition metal) are known since the 1970s [1] and are derived from the first “Na+ super-ionic conductor”, Na3Zr2Si2PO12, of this group of materials. The aims of current investigations are on the one hand the better understanding of the ionic conduction and on the other hand the search for new materials with very high ionic conductivity.
For this purpose, new and simple synthesis methods have been developed, which deliver very homogeneous powders with reduced temperatures for the preparation of ceramics. In this way a lithium ion conductor with the composition Li1.5Al0.5Ti1.5P3O12 was manufactured. After sintering to highly dense ceramics a total conductivity of 0.7 mS/cm was achieved at room temperature [2] and therefore this material belongs to the best known solid oxidic Li+ ion conductors. NMR and impedance spectroscopy investigations [3-5] have shown that the bulk conductivity amounts to 3-5 mS/cm and that the grain boundaries determine the quality of the material.
In the case of Na+ ion conductors, the prototype Na3Zr2Si2PO12 was newly synthesized and gave a previously not achieved conductivity of 1 mS/cm [6]. The modification of the composition by substitution with scandium delivered conductivities of 0.8 mS/cm (Na3.4Sc2Si0.4P2.6O12) [7] and 4 mS/cm (Na3.4Zr1.6Sc0.4Si2PO12) [8]. The latter composition possesses one of the highest known Na+ ion conductivities of oxide ceramics and reaches the conductivity of liquid electrolytes. The mentioned compositions confirm the empirical criteria which are necessary for achieving high ionic conductivities in NASICON materials [9].
References:
[1] H. Y. P. Hong, Mater. Res. Bull. 11 (1976) 173-182; H. Y. P. Hong, J. B. Goodenough, J. A. Kafalas, Mater. Res. Bull. 11 (1976) 203-220
[2] Q. Ma, Q. Xu, C.-L. Tsai, F. Tietz, O. Guillon, J. Am. Ceram. Soc., (2016), in press
[3] V. Epp, Q. Ma, F. Tietz, M. Wilkening, Phys. Chem. Chem. Phys., 17 (2015) 32115-32121
[4] S. Breuer, D. Prutsch, V. Epp, Q. Ma, F. Preishuber-Pflügl, F. Tietz, M. Wilkening, J. Mater. Chem. A, 3 (2015) 21343-21350
[5] D. Rettenwander, A. Welzl, S. Pristat, F. Tietz, S. Taibl, G. J. Redhammer, J. Fleig, J. Chem. Mater. A, 4 (2016) 1506-1513
[6] S. Naqash, Q. Ma, Tietz, O. Guillon, in preparation
[7] M. Guin, F. Tietz, O. Guillon, in preparation
[8] Q. Ma, M. Guin, S. Naqash, C.-L. Tsai, F. Tietz, O. Guillon, in preparation
[9] M. Guin, F. Tietz, J. Power Sources, 273 (2015) 1056-106
G Electronics and Data Acquisition (Forward-Angle Measurements)
The G parity-violation experiment at Jefferson Lab (Newport News, VA) is
designed to determine the contribution of strange/anti-strange quark pairs to
the intrinsic properties of the proton. In the forward-angle part of the
experiment, the asymmetry in the cross section was measured for
elastic scattering by counting the recoil protons corresponding to the two
beam-helicity states. Due to the high accuracy required on the asymmetry, the
G experiment was based on a custom experimental setup with its own
associated electronics and data acquisition (DAQ) system. Highly specialized
time-encoding electronics provided time-of-flight spectra for each detector for
each helicity state. More conventional electronics was used for monitoring
(mainly FastBus). The time-encoding electronics and the DAQ system have been
designed to handle events at a mean rate of 2 MHz per detector with low
deadtime and to minimize helicity-correlated systematic errors. In this paper,
we outline the general architecture and the main features of the electronics
and the DAQ system dedicated to G forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section
A. It has been written with Latex using \documentclass{elsart}. Nuclear
Instruments and Methods in Physics Research Section A: Accelerators,
Spectrometers, Detectors and Associated Equipment In Press (2007
Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering
We present the first measurements of the \vec{e}p->epg cross section in the
deeply virtual Compton scattering (DVCS) regime and the valence quark region.
The Q^2 dependence (from 1.5 to 2.3 GeV^2) of the helicity-dependent cross
section indicates the twist-2 dominance of DVCS, proving that generalized
parton distributions (GPDs) are accessible to experiment at moderate Q^2. The
helicity-independent cross section is also measured at Q^2=2.3 GeV^2. We
present the first model-independent measurement of linear combinations of GPDs
and GPD integrals up to the twist-3 approximation.Comment: 5 pages, 4 figures, 2 tables. Text shortened for publication.
References added. One figure remove
Deeply Virtual Compton Scattering off the neutron
The present experiment exploits the interference between the Deeply Virtual
Compton Scattering (DVCS) and the Bethe-Heitler processes to extract the
imaginary part of DVCS amplitudes on the neutron and on the deuteron from the
helicity-dependent D cross section measured at =1.9
GeV and =0.36. We extract a linear combination of generalized parton
distributions (GPDs) particularly sensitive to , the least constrained
GPD. A model dependent constraint on the contribution of the up and down quarks
to the nucleon spin is deduced.Comment: Published in Phys. Rev. Let
The E00-110 experiment in Jefferson Lab's Hall A: Deeply Virtual Compton Scattering off the Proton at 6 GeV
We present final results on the photon electroproduction
() cross section in the deeply virtual Compton
scattering (DVCS) regime and the valence quark region from Jefferson Lab
experiment E00-110. Results from an analysis of a subset of these data were
published before, but the analysis has been improved which is described here at
length, together with details on the experimental setup. Furthermore,
additional data have been analyzed resulting in photon electroproduction cross
sections at new kinematic settings, for a total of 588 experimental bins.
Results of the - and -dependences of both the helicity-dependent and
helicity-independent cross sections are discussed. The -dependence
illustrates the dominance of the twist-2 handbag amplitude in the kinematics of
the experiment, as previously noted. Thanks to the excellent accuracy of this
high luminosity experiment, it becomes clear that the unpolarized cross section
shows a significant deviation from the Bethe-Heitler process in our kinematics,
compatible with a large contribution from the leading twist-2 DVCS term to
the photon electroproduction cross section. The necessity to include
higher-twist corrections in order to fully reproduce the shape of the data is
also discussed. The DVCS cross sections in this paper represent the final set
of experimental results from E00-110, superseding the previous publication.Comment: 48 pages, 32 figure
Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime
We present measurements of the ep->ep pi^0 cross section extracted at two
values of four-momentum transfer Q^2=1.9 GeV^2 and Q^2=2.3 GeV^2 at Jefferson
Lab Hall A. The kinematic range allows to study the evolution of the extracted
hadronic tensor as a function of Q^2 and W. Results will be confronted with
Regge inspired calculations and GPD predictions. An intepretation of our data
within the framework of semi-inclusive deep inelastic scattering has also been
attempted
Microstructure evaluation of titanate based layered perovskites: Constrained vs. free sintering
Sem resum
Energy Linearity and Resolution of the ATLAS Electromagnetic Barrel Calorimeter in an Electron Test-Beam
A module of the ATLAS electromagnetic barrel liquid argon calorimeter was
exposed to the CERN electron test-beam at the H8 beam line upgraded for
precision momentum measurement. The available energies of the electron beam
ranged from 10 to 245 GeV. The electron beam impinged at one point
corresponding to a pseudo-rapidity of eta=0.687 and an azimuthal angle of
phi=0.28 in the ATLAS coordinate system. A detailed study of several effects
biasing the electron energy measurement allowed an energy reconstruction
procedure to be developed that ensures a good linearity and a good resolution.
Use is made of detailed Monte Carlo simulations based on Geant which describe
the longitudinal and transverse shower profiles as well as the energy
distributions. For electron energies between 15 GeV and 180 GeV the deviation
of the measured incident electron energy over the beam energy is within 0.1%.
The systematic uncertainty of the measurement is about 0.1% at low energies and
negligible at high energies. The energy resolution is found to be about 10%
sqrt(E) for the sampling term and about 0.2% for the local constant term
- …