Caractérisation par spectrométrie Mössbauer d’un oxy-hydroxyde ferrique mono-feuillet et de ses minéraux connexes: évidence d’un désordre structural

Abstract : Deviations of the magnetic properties of iron oxides of small particles size (or poorly crystallized minerals) from those of their bulk counterparts lead to radical changes in the appearance of their Mössbauer spectra. In Mössbauer spectroscopy, the poor crystallinity is mainly reflected by superparamagnetic properties. As a consequence, the magnetic transition (sextet-doublet transition) occurs at much lower temperatures than in the well-crystallized case. Here, specific examples of poorly crystallized Fe(III) oxides and related minerals are presented and characterized by Mössbauer and Raman spectroscopy. Among these examples, we have focused on Single Sheet Iron oxides (SSI), a novel type of single sheet materials [1-2] synthesized by anion exchanging layered Green Rust chloride (GRCl) with dodecanoate, followed by solid state oxidation to form ferric double hydroxide and subsequently delaminated by dispersion in sodium hydroxide. Spectra of SSI were collected from room temperature to 9 K in order to distinguish unambiguously between SSI and other ferric oxides such as ferrihydrite, ferric green rust or feroxyhite. SSI at room temperature shows a paramagnetic behavior with hyperfine parameters similar to those of ferric GR and ferrihydrite. By comparing these spectra with those of the ferric oxides, one can see that the low temperature measurements eliminate all relaxation effects and temperature dependence is faster for the SSI than for the ferrihydrite. The magnetic ordering of SSI starts at 130 K, the corresponding spectrum displaying broad lines. A recent preliminary study on the ferric green rust seems to show a similar behavior with an analysis performed in the same temperature range as SSI but with a slightly slower magnetic transition temperature; the start of the relaxation effect occurs at 100 K for ferric GR against 130 K for SSI while the ferrihydrite starts to relax below 60 K. This Mössbauer study is coherent with Raman spectra obtained for the same materials and confirms that both poor crystallinity and the high degree of structural disorder followed the sequence: ferrihydrite > ferric GR > SSI.
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Poster communications
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https://hal.archives-ouvertes.fr/hal-01559405
Contributor : Mustapha Abdelmoula <>
Submitted on : Tuesday, July 18, 2017 - 11:15:39 AM
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Mustapha Abdelmoula, Z Yin, L Huang, H Hansen, C Carteret, et al.. Caractérisation par spectrométrie Mössbauer d’un oxy-hydroxyde ferrique mono-feuillet et de ses minéraux connexes: évidence d’un désordre structural. 39ème journée du Groupe Francophone de Spectrométrie Mössbauer, May 2017, Beni Mellal Maroc. ⟨hal-01559405⟩

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