Mathieu Duttine

Dramatic Solid-State Humidity-Induced Modification of the Magnetic Coupling in a Dimeric Fluorous Copper(II)−Carboxylate Complex

The very fast and efficient water vapor absorption of the dimeric fluorous copper(II)-carboxylate complex [Cu(2)(C(8)F(17)CO(2))(4)(acetone)(2)] (1) leads, in the solid state, to a dramatic decrease of the exchange magnetic coupling between the copper(II) ions and to a drastic change of its powder EPR spectrum.

Local organization of Fe3+ into nano-CeO2 with controlled morphologies and its impact on reducibility properties

Ce and Fe are the main metal additives which have been tested by many laboratories for their catalytic activity at low temperature for soot oxidation in diesel engines.The key role and impact of Fe on the reducibility properties of ceria have been investigated on the basis of composition and structural features considering various synthesis routes. Two different procedures were used to prepare iron-substituted cerium dioxide Ce1−xFexO2−x/2: a classical co-precipitation route followed by annealing at T = 600 °C and an unusual microwave-assisted hydrothermal synthesis at T = 200 °C. The highest surface areas around 100 m2 g−1, have been obtained for oxides containing the largest Fe amount and prepared by the microwave-assisted route. Solid solutions were obtained up to x = 0.15 and 0.20 through microwave-assisted and co-precipitation routes, respectively. The highest decrease of the lattice parameter is observed for compounds prepared by the microwave-assisted route. The TEM analysis reveals a nano-cubic shape (with mainly {001} planes) for compounds prepared by the microwave-assisted route and containing low Fe amount. For the other compounds prepared also by the co-precipitation process, a nano-polyhedron shape corresponding to a thermodynamically stable morphology is observed. EPR (T = 5 K, very low Fe rates), Mossbauer (room temperature, x = 0.10) and XANES–EXAFS (RT and T = 20 K) spectroscopies studies showed that Fe ions adopt the trivalent state and are located in isolated distorted (orthorhombic and axial distortions) octahedra or form Fe clusters. The local organization of Fe3+ plays a key role in the oxygen vacancy distribution and consequently the reducibility properties of the Ce1−xFexO2−x/2 solid solution. For the compounds prepared by the microwave-assisted route, a large proportion of Fe3+ is located in isolated distorted octahedral sites that contribute to affect a high number of Ce4+ nearest neighbors with a high mobility of oxygen vacancies. In this case, the oxygen vacancies are well distributed around Ce4+ and Fe3+. In the case of compounds obtained by the co-precipitation route, Fe clusters abundance is higher and consequently oxygen vacancies are mainly located around Fe clusters. Such a distribution should explain the lower solubility limit and the larger variation of the cell parameter versus x Fe content in the series prepared by the microwave-assisted route. It is shown that these last compounds exhibit better reducibility properties with a doubled reduction rate (comparison between x(Fe) = 0.05 and pure CeO2) equal to 60% at T = 550 °C due to the iron local organization, a nano-cubic morphology and a higher surface area.

Anionic Ordering and Thermal Properties of FeF3·3H2O

Iron fluoride trihydrate can be used to prepare iron hydroxyfluoride with the hexagonal-tungsten-bronze (HTB) type structure, a potential cathode material for batteries. To understand this phase transformation, a structural description of β-FeF3·3H2O is first performed by means of DFT calculations and Mössbauer spectroscopy. The structure of this compound consists of infinite chains of [FeF6]n and [FeF2(H2O)4]n. The decomposition of FeF3·3H2O induces a collapse and condensation of these chains, which lead to the stabilization, under specific conditions, of a hydroxyfluoride network FeF3-x(OH)x with the HTB structure. The release of H2O and HF was monitored by thermal analysis and physical characterizations during the decomposition of FeF3·3H2O. An average distribution of FeF4(OH)2 distorted octahedra in HTB-FeF3-x(OH)x was obtained subsequent to the thermal hydrolysis/olation of equatorial anionic positions involving F(-) and H2O. This study provides a clear understanding of the structure and thermal properties of FeF3·3H2O, a material that can potentially bridge the recycling of pickling sludge from the steel industry by preparing battery electrodes.

Caractérisation par résonance paramagnétique électronique (RPE) de quartz naturels issus de différentes sources

Abstract Natural quartz crystals coming from Madagascar, Angola, Brazil, and Spain were studied by EPR after β irradiation in order to characterise the paramagnetic centres due to impurities, and examine in which way their relative proportion could constitute a useful criterion for origin researches. In all our samples, EPR experiments revealed germanium centres [GeO4/M+]° with M = Li or Na, aluminium ones [AlO4/h]° and two titanium centres ([TiO4/H+]° and [TiO4/M+]°) also appeared, except for samples coming from Spain. The comparison of the relative concentrations of paramagnetic species led us on to draw diagrams that allowed distinguishing the origins of the studied samples using only EPR spectra. To cite this article: M. Duttine et al., C. R. Geoscience 334 (2002) 949–955.

Comprehensive study of oxygen storage in YbFe2O4+x (x ≤ 0.5): unprecedented coexistence of FeOn polyhedra in one single phase

The multiferroic LuFe2.5+2O4 was recently proposed as a promising material for oxygen storage due to its easy reversible oxidation into LuFe3+2O4.5. We have investigated the similar scenario in YbFe2O4+x, leading to a slightly greater oxygen storage (OSC) capacity of 1434 μmol O/g. For the first time, the structural model of LnFe2O4.5 was fully understood by high-resolution microscopy images, and synchrotron and neutron diffraction experiments, as well as maximum entropy method. The oxygen uptake promotes a reconstructive shearing of the [YbO2] sub-units controlled by the adaptive Ln/Fe oxygen coordination and the Fe2/3+ redox. After oxidation, the rearrangement of the Fe coordination polyhedra is unique such that all available FeOn units (n = 6, 5, 4 in octahedra, square pyramids, trigonal bipyramids, tetrahedra) were identified in modulated rows growing in plane. This complex pseudo-ordering gives rise to short-range antiferromagnetic correlation within an insulating state.

Structural and Morphological Description of Sn/SnOx Core–Shell Nanoparticles Synthesized and Isolated from Ionic Liquid

The potential application of high capacity Sn-based electrode materials for energy storage, particularly in rechargeable batteries, has led to extensive research activities. In this scope, the development of an innovative synthesis route allowing to downsize particles to the nanoscale is of particular interest owing to the ability of such nanomaterial to better accommodate volume changes upon electrochemical reactions. Here, we report on the use of room temperature ionic liquid (i.e., [EMIm+][TFSI-]) as solvent, template, and stabilizer for Sn-based nanoparticles. In such a media, we observed, using Cryo-TEM, that pure Sn nanoparticles can be stabilized. Further washing steps are, however, mandatory to remove residual ionic liquid. It is shown that the washing steps are accompanied by the partial oxidation of the surface, leading to a core-shell structured Sn/SnOx composite. To understand the structural features of such a complex architecture, HRTEM, Mössbauer spectroscopy, and the pair distribution function were employed to reveal a crystallized β-Sn core and a SnO and SnO2 amorphous shell. The proportion of oxidized phases increases with the final washing step with water, which appeared necessary to remove not only salts but also the final surface impurities made of the cationic moieties of the ionic liquid. This work highlights the strong oxidation reactivity of Sn-based nanoparticles, which needs to be taken into account when evaluating their electrochemical properties.

Influence of hydrogenation and mechanical grinding on the structural and ferromagnetic properties of GdFeSi

Abstract Hydrogen insertion into GdFeSi induces (i) a structural transition from a tetragonal CeFeSi-type to a tetragonal ZrCuSiAs-type, (ii) an anisotropic expansion of the unit cell parameters because the a parameter decreases, whereas the c parameter increases, and (iii) a decrease in Curie temperature from 121 to 20 K. On the contrary, an amorphous ferromagnet (TC = 65 K) is obtained by mechanical grinding of GdFeSi. The three compounds (GdFeSi, GdFeSiH, and amorphous GdFeSi) were investigated by 57Fe Mössbauer spectroscopy. At 4.2 K, this study has revealed that the magnetically ordered Gd substructure produces a small transferred hyperfine magnetic field at the 57Fe nucleus.