期刊
CLAY MINERALS
卷 44, 期 1, 页码 19-34出版社
MINERALOGICAL SOC
DOI: 10.1180/claymin.2009.044.1.19
关键词
ferrihydrite; feroxyhite; structure; PDF; XRD; EXAFS spectroscopy; bond valence
资金
- Office of Energy Research
- Office of Basic Energy Sciences
- Materials Sciences Division of the U.S, Department of Energy, [DE-AC02-050CH11231]
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 lambda = 0.137 angstrom. The new ferrihydrite model is isostructural to akdalaite (Al10O14(OH)(2)) a mineral having the Baker-Figgis delta-isomer of the Al-13-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 (Fe-VI(4+)), 20% divalent tetrahedral iron (Fe-IV(2+)), and some Fe-IV-O distances equal to or larger than the Fe-VI(3+)-O distances, thus violating Pauling's 2(nd) 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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