Ferrihydrite electron diffraction pattern

Highly-broadened XRD peaks and electron diffraction patterns indicate that ferrihy-drites are characterized by small crystal size and/or low structural order. TEM shows single spherical particles, ca. 4-6 nm in size (Fig. 4.17). At higher magnification (HRTEM), 6-line ferrihydrite appeared as single crystals with a hexagonal outline and... 

Like X-ray diffraction patterns, neutron and electron diffraction patterns provide averaged information about the structure of a compound. Details of these techniques are given in works by Hirsch et al. (1965) and West (1988). Neutron diffraction involves interaction of neutrons with the nuclei of the atoms. As the neutrons are scattered relatively evenly by all the atoms in the compound, they serve to indicate the positions of the protons in an oxide hydroxide. This technique has been applied to elucidation of the structure and/or magnetic properties of goethite (Szytula et al., 1968 Forsyth et al., 1968), akaganeite (Szytula et al., 1970), lepidocrocite (Oles et al., 1970 Christensen Norlund-Christensen, 1978), hematite (Samuelson Shirane, 1970 Fernet et al., 1984) and wiistite (Roth, 1960 Cheetham et al., 1971 Battle Cheetham, 1979). A neutron diffractogram of a 6-line ferrihydrite was recently produced by Jansen et al. (2002) and has helped to refine its structure (see chap. 2). 

The generally accepted structure for the crystalline iron core of ferritin is the ferrihydrite structure proposed by Towe Bradley.This consists of oxygen layers with iron in octahedral sites between the layers. Ford et al and PowelF have sununarized the evidence in support of this model for ferritin, which includes electronic spectroscopic data and EXAFS measurements confirming the presence of six-coordinate Fe(III) and indicating that four-coordinate Fe(III) is present, if at aU, at low levels only. This latter point is important because the X-ray powder diffraction patterns of... 

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