34 research outputs found
Structural and electrical properties of ceramic Li-ion conductors based on LiAlTi(PO)-LiF
The work presents the investigations of Li1.3Al0.3Ti1.7(PO4)3-xLiF Li-ion
conducting ceramics with 0 < x < 0.3 by means of X-ray diffractometry (XRD),
7Li, 19F, 27Al and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS
NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM),
impedance spectroscopy (IS) and density method. It has been shown that the
total ionic conductivity of both as-prepared and ceramic Li1.3Al0.3Ti1.7(PO4)3
is low due to a grain boundary phase exhibiting high electrical resistance.
This phase consists mainly of berlinite crystalline phase as well as some
amorphous phase containing Al3+ ions. The electrically resistant phases of the
grain boundary decompose during sintering with LiF additive. The processes
leading to microstructure changes and their effect on the ionic properties of
the materials are discussed in the frame of the brick layer model (BLM). The
highest total ionic conductivity at room temperature was measured for
LATP-0.1LiF ceramic sintered at 800{\deg}C and was equal to {\sigma}tot = 1.1 x
10-4 Scm-1
Impact of LiBSO glass additive on the structure and electrical properties of the LATP-based ceramics
The existing solid electrolytes for lithium ion batteries suffer from low
total ionic conductivity, which restricts its usefulness for the lithium-ion
battery technology. Among them, the NASICON-based materials, such as
Li1.3Al0.3Ti1.7(PO4)3 (LATP) exhibit low total ionic conductivity due to highly
resistant grain boundary phase. One of the possible approaches to efficiently
enhance their total ionic conductivity is the formation of a composite
material. Herein, the Li2.9B0.9S0.1O3.1 glass, called LBSO hereafter, was
chosen as an additive material to improve the ionic properties of the ceramic
Li1.3Al0.3Ti1.7(PO4)3 base material. The properties of this
Li1.3Al0.3Ti1.7(PO4)3-xLi2.9B0.9S0.1O3.1 (0 < x < 0.3) system have been studied
by means of high temperature X-ray diffractometry (HTXRD), 7Li, 11B, 27Al and
31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR),
thermogravimetry (TG), scanning electron microscopy (SEM), impedance
spectroscopy (IS) and density methods. We show here that the introduction of
the foreign LBSO phase enhances their electric properties. This study reveals
several interesting correlations between the apparent density, the
microstructure, the composition, the sintering temperature and the ionic
conductivity. Moreover, the electrical properties of the composites will be
discussed in the terms of the brick-layer model (BLM). The highest value of
{\sigma}tot = 1.5 x 10-4 Scm-1 has been obtained for LATP-0.1LBSO material
sintered at 800{\deg}C
Properties of LiMnBO3 glasses and nanostructured glass-ceramics
Polycrystalline LiMnBO3 is a promising cathode material for Li-ion batteries.
In this work, we investigated the thermal, structural and electrical properties
of glassy and nanocrystallized materials having the same chemical composition.
The original glass was obtained via a standard meltquenching method. SEM and
7Li solid-state NMR indicate that it contains a mixture of two distinct glassy
phases. The results suggest that the electrical conductivity of the glass is
dominated by the ionic one. The dc conductivity of initial glass was estimated
to be in the order of 10-18 S.cm-1 at room temperature. The thermal
nanocrystallization of the glass produces a nanostructured glass-ceramics
containing MnBO3 and LiMnBO3 phases. The electric conductivity of this
glass-ceramics is increased by 6 orders of magnitude, compared to the starting
material at room temperature. Compared to other manganese and borate containing
glasses reported in the literature, the conductivity of the nanostructured
glass ceramics is higher than that of the previously reported glassy materials.
Such improved conductivity stems from the facilitated electronic transport
along the grain boundaries
Residual entropy and spin gap in a one-dimensional analog of the pyrochlore antiferromagnet
We show that the low-energy sector of the S=1/2, antiferromagnetic Heisenberg
model on a one-dimensional lattice of coupled tetrahedra consists of 2^N
replica of the spectrum of the dimerized Heisenberg chain, where N is the
number of tetrahedra.
This provides a proof of the following properties: i) there is a residual
ground-state entropy per spin equal to 2^{1/4}; ii) there is a singlet-triplet
gap as long as the coupling between the tetrahedra is smaller than the internal
one. These properties are compared to available results on the pyrochlore
lattice.Comment: 4 pages with 3 figure
The D-HMQC MAS-NMR technique: An efficient tool for the editing of through-space correlation spectra between quadrupolar and spin-1/2 (<sup>31</sup>P, <sup>29</sup>Si, <sup>1</sup>H, <sup>13</sup>C) nuclei
The D-HMQC (dipolar heteronuclear multiple-quantum coherence) technique is a recently developed NMR pulse sequence particularly suitable for the investigation of spatial proximity between quadrupolar and spin-1/2 nuclei. Compared to the cross-polarisation magic-angle spinning technique applied to a quadrupolar nucleus, D-HMQC does not require time-consuming optimisations and exhibits on the quadrupolar spin a better robustness to irradiation offset and to Cq values and radiofrequency field. Furthermore, the high robustness to irradiation offset makes of the D-HMQC sequence the technique of choice for the structural characterisation of materials especially at high magnetic field. We show here how the D-HMQC can be easily implemented and optimised to give access to the structural analysis of silicate-, phosphate-, carbon- and proton-containing materials. An emphasis will be on describing the most popular dipolar recoupling schemes that can be used in that sequence and providing their advantages and drawbacks
Structural characterisation of phosphate materials: new insights into the spatial proximities between phosphorus and quadrupolar nuclei using the D-HMQC MAS NMR technique
International audienc
Observation of proximities between spin-1/2 and quadrupolar nuclei: Which heteronuclear dipolar recoupling method is preferable?
International audienc
Solvent-free high-field dynamic nuclear polarization of mesoporous silica functionalized with TEMPO
We report high-field magic-angle spinning dynamic nuclear polarization (MAS DNP) of mesoporous silica functionalized with nitroxide radicals. These results demonstrate that co-condensation can be employed to incorporate DNP polarizing agents into inorganic materials and that solvent-free DNP is feasible for porous materials. For the investigated material, the direct MAS DNP enhances the 29Si nuclear magnetic resonance (NMR) spectra, whereas the indirect MAS DNP via protons is inapplicable owing to the inefficiency of 1H → 29Si cross polarization transfer. Furthermore, the 29Si signals in direct experiments build up in a few seconds at 100 K. This fast polarization buildup improves the NMR sensitivity and will be useful for the investigation of direct DNP below 100 K
Double-quantum 19F-19F dipolar recoupling at ultra-fast magic angle spinning NMR: Apllication to the assignment of 19F spectra of inorganic fluorides
International audienc