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Article Dans Une Revue Physics and Chemistry of Minerals Année : 2015

Probing the local environment of substitutional Al3+ in goethite using X-ray absorption spectroscopy and first-principles calculations

Résumé

We present experimental and calculated Al K-edge X-ray absorption near-edge structure (XANES) spectra of aluminous goethite with 10 to 33 mol % of AlOOH and diaspore. Significant changes are observed experimentally in the near and pre-edge regions with increasing Al concentration in goethite. First-principles calculations based on density-functional theory (DFT) reproduce successfully the experimental trends. This permit to identify the electronic and structural parameters controlling the spectral features and to improve our knowledge of the local environment of Al3+ in the goethite-diaspore partial solid solution. In the near-edge region, the larger peak spacing in diaspore compared to Al-bearing goethite is related to the nature (Fe or Al) of the first cation neighbours around the absorbing Al atom (Al*). The intensity ratio of the two near-edge peaks, which decreases with Al concentration, is correlated with the average distance of the first cations around Al* and the distortion of the AlO6 octahedron. Finally, the decrease in intensity of the pre-edge features with increasing Al concentration is due to the smaller number of Fe atoms in the local environment of Al since Al atoms tend to cluster. In addition, it is found that the pre-edge features of the Al K-edge XANES spectra enable to probe indirectly empty 3d states of Fe. Energetic, structural and spectroscopic results suggest that for Al concentrations around 10 mol %, Al atoms can be considered as isolated whereas above 25 mol %, Al clusters are more likely to occur.
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hal-01262097 , version 1 (26-01-2016)

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Paternité - Pas d'utilisation commerciale - Pas de modification

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Manoj Ducher, Marc Blanchard, Delphine Vantelon, Ruidy Nemausat, Delphine Cabaret. Probing the local environment of substitutional Al3+ in goethite using X-ray absorption spectroscopy and first-principles calculations. Physics and Chemistry of Minerals, 2015, 43 (3), pp.217-227. ⟨10.1007/s00269-015-0788-z⟩. ⟨hal-01262097⟩
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