Cation Ordering in Synthetic Layered Double Hydroxides

M. Vucelic1, W. Jones1 and G. D. Moggridge2
1 Chemistry Department, University of Cambridge, Lensfield Rd., Cambridge CB2 1EW, United Kingdom
2 Chemical Engineering Department, University of Cambridge, Pembroke St., Cambridge CB2 3RA, United Kingdom

Abstract: A combined powder X-ray diffraction (XRD) and X-ray absorption (XAS) study of Fe(III) cation ordering within pyroaurite is described. It is concluded that there is no correlation between Fe(III) cation positions over distances of a few tens of angstroms, but that there is a very high level of local ordering, involving the absence of Fe(III)-Fe(III) neighbors. These observations are rationalized in terms of a significant frequency of lattice defects in the form of cation vacancies or Mg for Fe(III) substitutions. These results are expected to be generalizable to other M(II)/M(III) layered double hydroxides (LDHs), but are in contrast to the long-range cation ordering observed in Li/Al LDHs. This raises the interesting possibility of differing properties and stabilities based on the degree of cation ordering.

Key Words: Cation Ordering • LDH • Pyroaurite • XAS • XRD

Clays and Clay Minerals; December 1997 v. 45; no. 6; p. 803-813; DOI: 10.1346/CCMN.1997.0450604
© 1997, The Clay Minerals Society
Clay Minerals Society (www.clays.org)