Abstraet--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

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... 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 orderir~g observed in Li/AI LDHs. This raises the interesting possibility of differing properties and stabilities based on the degree of cation ordering.