Jean Marc Greneche

Structural and magnetic properties of barium hexaferrite nanostructured particles prepared by the combustion method

Abstract The combustion method, a fast and simple way of preparing sub-micrometer sized particles from a solution of the corresponding metal nitrates and a reducing agent (ODH, TFTA) which is used as a fuel, was adapted to the synthesis of barium hexaferrite particles. Structural and magnetic properties were investigated by X-ray diffraction, transmission electronic microscopy, magnetic measurements and Mossbauer spectrometry on nanostructured as well as on microstructured particles resulting from annealing treatments under different conditions. High values of the coercive field (5.3 kOe) and of the magnetization (57.8 emu/g), at 13.5 kOe, were obtained on well crystallized BaFe 12 O 19 particles annealed at 850°C.

[Fe2(C10O8H2)]: an antiferromagnetic 3D iron(II) carboxylate built from ferromagnetic edge-sharing octahedral chains (MIL-62).

The first three-dimensional iron(II) tetracarboxylate is built from the connection of chains of edge-sharing Fe(II) octahedra by 1,2,4,5-benzenetetracarboxylates; magnetic measurements show an antiferromagnetic coupling of ferromagnetic chains below TN = 25(1) K.

Hydrothermal synthesis, structure and magnetic properties of [Fe3(PO4)3F2, H3N(Ch2)4NH3]: The analog of the three-dimensional gallophosphate structure-type ULM-3

Abstract [Fe 3 (PO 4 ) 3 F 2 , H 3 N(CH 2 ) 4 NH 3 ] has been synthesized hydrothermally (453 K, 24 h, autogenous pressure). Its structure was determined by single-crystal X-ray diffraction. It is orthorhombic (space group Pbca No. 61) with cell parameters a = 10.203(1) A , b = 18.670(1) A , c = 16.268(1) A , V = 3099(1) A 3 and Z = 8 . Its three-dimensional structure, refined to R 1 ( F 0 ) = 0.036 and wR 2 ( F 2 0 ) = 0.093 from 6821 unique reflections ( l > 2 σ (1)) is isostructural with the oxyfluorinated gallophosphate ULM-3. From a structural point of view, this leads to 10-membered channels along [100]. It is also an antiferromagnetic compound which orders at T N = 37(2) K. Mossbauer data are consistent with the presence of two distinct Fe 3− sites in the high spin state: one corresponding to Fe 3− in an octahedral site and the other to two Fe 3+ in trigonal bipyramids. Magnetic couplings are discussed in terms of superexchange and supersuperexchange interactions.

Tuning the breathing behaviour of MIL-53 by cation mixing

A mixed cation MIL-53(Cr-Fe) MOF has been obtained by direct synthesis. Multiple experimental techniques have demonstrated the presence of a genuine mixed phase, leading to a breathing behaviour different from either of the single cation analogues.

Adsorption of As(III) on chitosan-Fe-crosslinked complex (Ch-Fe)

It was reported the adsorption of As(III) on the surface of the chitosan-Fe-crosslinked complex. Theoretical correlation of the experimental equilibrium adsorption data for As(III)/Ch-Fe system is best explained by the non-linearized form Langmuir-Freundlich isotherm model. At optimum conditions, pH 9.0, the maximum adsorption capacity, calculated using the Langmuir-Freundlich isotherm model was 13.4 mg g⁻¹. The adsorption kinetics of As(III) onto Ch-Fe are described by the pseudo-first-order kinetic equation. The results of the Mössbauer spectroscopy showed that there is no redox process on the surface of the adsorbent.

Surface effects in CoFe2O4 magnetic fluids studied by Mössbauer spectrometry

Abstract Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mossbauer spectrometry. The studies include superparamagnetic (SP) relaxation as well as the surface phenomena of samples with different particle sizes both in the form of ferrofluids and powders. A core–shell model was applied to estimate the thickness of the surface “spin-canted” shell around particles.

Intracellular biosynthesis of superparamagnetic 2-lines ferri-hydrite nanoparticles using Euglena gracilis microalgae

The intracellular biosynthesis of superparamagnetic (blocking temperature 5.6K) 2-lines ferrihydrite (Fh2L) nanoparticles was observed within living Euglena gracilis microalgae.

Synthesis and morphological characterization of nanocrystalline powders obtained by a gas condensation method

Abstract The preparation of nanocrystalline powders of Fe and Fe50Ni50 has been performed by a gas-condensation method under pure helium atmosphere. The characterization of the prepared materials which was carried out by means of Transmission Electron Microscopy, X-rays diffraction and Mossbauer Spectrometry, evidences for the presence of oxide phases. Fe and FeNi based ultrafine particles are observed with a size comprised within the range 10–70 nm and they occur as clusters or chains.

New A-deficient perovskites in the series LixLa2/3Ti1-xFexO3 (0.12 ≤ x ≤ 0.33) and La(2+x)/3Ti1-xFexO3 (0.5 ≤ x ≤ 1.0)

Two new series of A-deficient perovskites have been synthesized and structurally characterized from Rietveld treatment of their X-ray diffraction powder patterns. The first one, LixLa2/3Ti1-xFexO3, for 0.12 ≤ x ≤ 0.33, results from the substitution mechanism Ti4+ → Fe3+ + Li+. The structure is closely related to that of La2/3-xLi3xTiO3 (a ≈ ap, b ≈ ap and c ≈ 2 ap) with a symmetry evolution leading to the existence of two domains: for 0.12 ≤ x ≤ 0.19 the symmetry is orthorhombic (Pmmm), while for 0.20 ≤ x ≤ 0.33 a tetragonal symmetry is obtained (P4/mmm). In both cases, the population of La3+ ions, unequally distributed on two adjacent sites for smaller x values, is directly affected by the increase of the Li content and tends to be equalized with larger x values. The second series is found to result from another substitution mechanism Ti4+ → Fe3+ + 1/3La3+, leading to the formula La(2+x)/3Ti1-xFexO3 in the domain 0.5 ≤ x ≤ 1.0. The structure is then closely related to that of LaFeO3, where La3+ ions occupy now only one crystallographic site in the Pnma space group. Transmission Electron Microscopy and Mossbauer spectrometry confirm the above models.

Synthesis and characterization of small BaFe12O19 particles

Abstract Fine particles of BaFe 12 O 19 have been successfully prepared using a combustion method and annealed at 700, 750, 850 and 1000°C to obtain particles with average diameter in the range 50–200 nm. The structural properties observed by X-ray diffraction in conjunction with the hyperfine characteristics estimated from room temperature Mossbauer spectra explain well the magnetic behavior of the small particles.