Pierre Strobel

Structure-Properties Relationships of Lithium Electrolytes Based on Ionic Liquid

Low-melting ionic liquid, IL, based on small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), where R(1), R(2), R(3) = CH(3) or C(2)H(5), R = C(3)H(7), C(4)H(9), C(6)H(13), C(8)H(17), CF(3)C(3)H(6)) and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs, including melting point, glass transition, and degradation temperatures; viscosity; density; ionic conductivity; diffusion coefficient; and electrochemical stability, were determined. Heteronuclear Overhauser NMR spectroscopy experiments were also performed to point out the presence of pair correlation between the different moieties. The LiTFSI addition effect on the IL properties was studied with the same methodology. Some nanoscale organization with segregation of polar and apolar domains was observed. ILs with small alkyl chain length or fluorinated ammonium exhibit very high electrochemical stability in oxidation.

Structure solution of the new titanate Li4Ti8Ni3O21 using precession electron diffraction

A sample having stoichiometry Li[Ti(1.5)Ni(0.5)]O(4) has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910 (1), c = 32.5371 (1) A. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group P3c1. The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li(4)Ti(8)Ni(3)O(21), which is compatible with the microanalysis results.

Fe3+ spin transition in CaFe2O4 at high pressure

Abstract Single-crystal diffraction data collected for CaFe2O4 at high pressure reveal above 50 GPa an isosymmetric phase transition (i.e., no change in symmetry) marked by a volume decrease of 8.4%. X-ray emission spectroscopic data at ambient and high pressure confirm that the nature of the phase transition is related to the Fe3+ high-spin/low-spin transition. The bulk modulus K0 calculated with a Birch Murnaghan EoS (K′ = 4) is remarkably different [K0 = 159(2) GPa for CaFe2O4 “high spin” and K0 = 235(10) GPa for CaFe2O4 “low spin”]. Crystal structure refinements reveal a decrease of 12% of the Fe3+ crystallographic site volume. The geometrical features of the low-spin Fe3+ crystallographic site at high pressure (bond lengths, volume) indicate a relevant decrease of Fe3+-O bond lengths, and the results are in agreement with tabulated values for crystal radii of Fe3+ in high- and low-spin state. The reduced crystal size of Fe3+ in the low-spin state suggest that in lower mantle assemblages, Fe3+ partitioning in crystallographic sites should be strongly affected by the iron spin state.

Electrolyte based on fluorinated cyclic quaternary ammonium ionic liquids

Ionic liquids, ILs, based on fluorinated pyrrolidinium and piperidinium ammonium cations and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs including melting point, glass transition and degradation temperatures, viscosity, ionic conductivity, and electrochemical stability were determined and compared to alkyl pyrrolidinium and piperidinium ILs. The incorporation of a CF3 group instead of a CH3 induces an increase of the IL viscosity, thus a conductivity decrease. However, good ionic conductivity is obtained with fluorinated pyrrolidinium IL. Cyclic amine ILs with propyl alkyl chain or fluorinated ammonium exhibit very high electrochemical stability toward oxidation. The effect of the addition of LiTFSI on the IL properties was studied with the same methodology.

Structural and Magnetic Properties of Substituted Delafossite-Type Oxides CuCr 1−x Sc x O 2

This work describes the scandium doping effect on the structural and magnetic properties of delafossite-type oxides CuCr1 － xScxO2. The lattice parameters were found to vary according to Vegard’s low. A reflection broadening is observed, that is ascribed to local lattice distortion due to the ionic radius difference between Cr3+ and the non-magnetic dopants. Magnetic susceptibility measurements show that the dominant interactions are antiferromagnetic (AFM) but that doping induces significant changes. The coupling between the local spins at the Cr sites and doped metal transition may enhance spin fluctuations at the Cr sites, which break the residual magnetic degeneracy as fluctuation-induced symmetry breaking in a highly magnetic degenerate ground state manifold of some frustrated systems.

Structural, magnetic and electric properties of Delafossite-type oxide, Cu1-xAgxCrO2 (0 < x < 0.5)

Polycrystalline samples of the delafossite Cr oxide Cu1−xAgxCrO2 were investigated to clarify its transport properties. The synthetized phases are found to contain a slight oxygen excess (δ = 0.06). The valence state of the Cr ions in the Cu1−xAgxCrO2 samples was identified as >3+ by analysing their TGA spectra, their lattice parameters and their electrical properties. The temperature dependence of zerofield-cooling magnetization was measured. All samples exhibits paramagnetic behaviour at high temperature. At low temperature they exhibit a clear ferromagnetic (FM) transition around 130 K. For x = 0.10 the samples exhibit an AFM transition at 25K. Clear hysteresis loops indicate that FM order exists in the Ag-doped samples at 2 K. All samples behave like semiconductors.

Synthesis, structural and magnetic studies of the CuCr{sub 1-x}Rh{sub x}O{sub 2} delafossite solid solution with 0 {<=} x {<=} 0.2

Highlights: {yields} Rh non-magnetic replacement of the Cr in the magnetic frustrated delafossite CuCrO{sub 2}. {yields} Delafossite solid solution is maintained up to 0.2 in this system. {yields} Strain generated by Rh substitution is strongly anisotropic. {yields} M{sup 3+}-O bond strength is affected. {yields} High temperature paramagnetic behavior and weak ferromagnetism at low temperature. -- Abstract: The CuCr{sub 1-x}Rh{sub x}O{sub 2} series is investigated by X-ray diffraction, magnetization measurements and Raman spectroscopy on ceramic samples. It is found that a delafossite solid solution is maintained up to x = 0.2 in CuCr{sub 1-x}Rh{sub x}O{sub 2}. The small observed variation in cell parameters is consistent with the small difference between the ionic radii of Cr{sup 3+} and Rh{sup 3+}. A significant broadening of X-ray reflections is observed and when analyzed using the Williamson-Hall relationship showed that the strain generated by Rh substitution is strongly anisotropic, affecting mainly (Cr,Rh)-O bonds in the ab plane. Room temperature Raman spectra displayed three main Raman active modes. All modes shift to lower frequency and undergo significant changes in intensity with increasing Rh content, showing the effect of Rh atoms on the M{sup 3+}-O bond strength. The magnetic behavior of CuCr{sub 1-x}Rh{sub x}O{sub 2} samples wasmorexa0» investigated as a function of temperature and applied field. At high temperature paramagnetic behavior, and at low temperature, evidence for weak ferromagnetism, reinforced by a hysteresis loop at 4 K is observed. The magnetic behavior of CuCr{sub 1-x}Rh{sub x}O{sub 2} is attributed to the disorder of Cr and Rh in octahedral sites resulting in short-range Cr-O-Cr and Cr-O-Rh interactions, which give rise to short-range weak ferromagnetism.«xa0less