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XRD peak migration and apparent shift of cell-edge lengths of nano-sized hematite, goethite and lepidocrocite

H. STANJEK^*,

Lehrstuhl für Bodenkunde, TU München, 85350 Freising, Germany

^* E-mail: stanjek{at}iml.rwth-aachen.de

(Received 2 July 2001; revised 31 January 2002)

X-ray powder diffraction patterns were simulated for nano-sized hematite, goethite and lepidocrocite by three-dimensional integration in reciprocal space. The cell-edge lengths were refined together with the size parameters X and X_e of the Thompson-Cox-Hastings function, which for orthorhombic structures was extended by a biaxial broadening parameter X_o. Variations of the structure factors across broad peaks resulted in apparent peak shifts and concomitant shifts in cell-edge lengths, which were significantly correlated with the size parameters for hematite and partially correlated for goethite and lepidocrocite. Regression equations are given for correcting cell-edge lengths obtained from Rietveld fits for size-induced shifts.

KEYWORDS: goethite, hematite, lepidocrocite, XRD, cell-edge lengths, peak shift, nano particles