Evaluation of the structural model for ferrihydrite derived from real-space modelling of high-energy X-ray diffraction data - Archive ouverte HAL Access content directly
Journal Articles Clay Minerals Year : 2009

Evaluation of the structural model for ferrihydrite derived from real-space modelling of high-energy X-ray diffraction data

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Abstract

A new structural model for ferrihydrite that challenges the standard ferrihydrite model established by X-ray diffraction and confirmed by neutron diffraction and single-crystal electron nanodiffraction was recently proposed by Michel et al. (2007a) from the simulation of the pair distribution function obtained by Fourier transformation of diffraction data measured at l = 0.137 A ˚ . The new ferrihydrite model is isostructural to akdalaite (Al10O14(OH)2), a mineral having the Baker-Figgis d-isomer of the Al13-Keggin structure as its structural motif. The new model is unrealistic because: (1) it is completely periodic (i.e. defect-free); (2), it has 20% tetravalent octahedral iron (VIFe4+), 20% divalent tetrahedral iron (IVFe2+), and some IVFeO distances equal to or larger than the VIFe3+O distances, thus violating Pauling's 2nd rule; (3) it does not describe X-ray diffraction and EXAFS spectroscopic data; and, (4) it is inconsistent with electron microscopy results and contradicts previous X-ray scattering studies.
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Dates and versions

insu-00411781 , version 1 (28-08-2009)

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Alain Manceau. Evaluation of the structural model for ferrihydrite derived from real-space modelling of high-energy X-ray diffraction data. Clay Minerals, 2009, 44 (1), pp.19-34. ⟨10.1180/claymin.2009.044.1.19⟩. ⟨insu-00411781⟩
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