Structure of synthetic 2-line ferrihydrite by electron nanodiffraction

D. E. Janney, J. M. Cowley, P R Buseck

Research output: Contribution to journalArticle

125 Citations (Scopus)

Abstract

Comparison of experimental single-crystal electron diffraction patterns of synthetic two-line ferrihydrite (2LFh) with simulated single-crystal electron-diffraction patterns indicates that a synthetic 2LFh sample contains highly disordered material and nanocrystals with structures based on hexagonal (ABAB) and cubic (ABC) stacking of close-packed layers of O2- and OH- ions. An apparently continuous variation in ordering exists between the highly disordered material and each of the crystalline structures, suggesting that both nanocrystalline structures represent local extremes of three-dimensional ordering. Experimental diffraction patterns were obtained using electron nanodiffraction, a technique in which the finely focused beam from a field-emission gun in an electron microscope can be used to produce diffraction patterns from areas <1 nm across. Nanodiffraction patterns from the highly disordered material have diffuse streaks rather than distinct reflections, and are consistent with a two-dimensional structure that consists of close-packed anionic layers with essentially complete stacking disorder and nearly random distribution of Fe atoms. The structure with cubic stacking is similar to maghemite and has ~25% of the Fe in tetrahedral sites. The structure with hexagonal stacking consists of double chains of face-sharing Fe octahedra; each octahedron shares one face, two edges, and three corners with adjacent octahedra. Previous results from transmission electron microscopy, powder X-ray and electron diffraction, and synchrotron-based techniques reflect the overall high degree of structural disorder rather than the characteristics of the maghemite-like and double-chain structures.

Original languageEnglish (US)
Pages (from-to)1180-1187
Number of pages8
JournalAmerican Mineralogist
Volume85
Issue number9
StatePublished - 2000

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ferrihydrite
Diffraction patterns
diffraction
diffraction patterns
stacking
Electron diffraction
electron
electron diffraction
Electrons
maghemite
electrons
Single crystals
disorders
nanostructure (characteristics)
crystal
single crystals
statistical distributions
Synchrotrons
Field emission
Powders

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Structure of synthetic 2-line ferrihydrite by electron nanodiffraction. / Janney, D. E.; Cowley, J. M.; Buseck, P R.

In: American Mineralogist, Vol. 85, No. 9, 2000, p. 1180-1187.

Research output: Contribution to journalArticle

Janney, D. E. ; Cowley, J. M. ; Buseck, P R. / Structure of synthetic 2-line ferrihydrite by electron nanodiffraction. In: American Mineralogist. 2000 ; Vol. 85, No. 9. pp. 1180-1187.
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