Anomalous Valence Contrast of Metal Transition in Nanocrystalline Ferrite

Cation Distribution in a Titanium Ferrite Fe2.75Ti0.25O4Measured byin-SituAnomalous Powder Diffraction Using Rietveld Refinement

Many ferrites contain different cations with various valence states and location in the spinel structure. In compounds such as these, only a combination of different techniques such as Mussbauer spectroscopy, IR analysis, and thermogravimetry allows the distribution of cations to be obtained. For very complicated distributions, the mathematical decomposition of derivative thermogravimetric curves (DTG) leading to quantitative distribution is uncertain. In this paper, we present an alternative technique based on resonant diffraction. The anomalous scattering of each cation in the crystalline material is used to determine its amount and position by Rietveld refinement. Since the energy for su…

Utilisation de la diffraction résonnante pour déterminer la distribution cationique d'un ferrite de titane nanométrique

Les proprietes magnetiques des ferrites de structure spinelle dependent, entre autres, de la distribution cationique dans la maille. La connaissance de cette repartition a pu etre obtenue dans le cas d'un ferrite substitue au titane en utilisant la diffraction anomale de poudre couplee avec un affinement structural de type Rietveld, methode qui est le fruit des dernieres avancees effectuees autour du rayonnement synchrotron.

Synchrotron diffraction study of the isothermal oxidation of uranium dioxide at 250°C

ABSTRACTThe structural evolution of UO2 during its oxidation to U3O8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases that are likely to appear during the long-term storage of spent nuclear fuel. Our results are in disagreement with the literature in which the existence of an intermediate cubic phase is not reported. Instead, an α-U3O7 tetragonal phase (c/a < 1) was mentioned but not definitively observed. These previous interpretations may have been the result of poor instrumental resolution.

Contribution of the synchrotron diffraction study of the oxidation of uranium dioxide at 250○C

The structural evolution of UO 2 during its oxidation into U 3 O 8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases which are likely to appear during a long term storage of used nuclear fuel. Our results are in disagreement with the literature where the existence of the secondary cubic phase is not reported, and an α-U 3 O 7 tetragonal phase (c/a < 1) is also mentioned but definitely not observed. These previous interpretations are possibly due to a poor instrumental resolution, inducing a sensible broadening of the diffraction peaks. Particularly, the fact that the instrumental resolution…

Diffraction anomale et composition cationique d'une titanomagnétite nanométrique

Les ferrites substitues au titane constituent des materiaux interessants pour aller vers la comprehension des reactions d'oxydo-reduction qui ont lieu dans ces composes de structure spinelle. Ces composes synthetises par chimie douce on ete etudies in-situ par diffraction anomale dans diverses conditions. Dans le cas particulier du compose Fe 2.5 Ti 0.5 O 4 , les premiers resultats montrent que cette methode de synthese ne permet pas d'elaborer directement le ferrite avec la composition esperee. En effet l'analyse structurale met en evidence un taux de titane bien inferieur a 0.5 alors que d'autres techniques,(analyse ICP, methode de Poix), confirment ce taux de substitution.