International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 3.5, p. 284

Section 3.5.3.2. Preferred-orientation effects

A. Le Baila*

aUniversité du Maine, Institut des Molécules et Matériaux du Mans, UMR CNRS 6283, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France
Correspondence e-mail: lebail@univ-lemans.fr

3.5.3.2. Preferred-orientation effects

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One has to ensure that preferred orientation is minimized during the recording of the powder pattern if the extracted |Fhkl| values are to be used for structure solution. In transmission geometry with a capillary specimen (provided that it is not composed of long needle-shaped particles that are all aligned), there is generally no problem. But in reflection geometry with samples pressed on the holder, preferred orientation is not rare, even if it is not obvious in the data. Collecting a second pattern from a sample dusted onto the holder through a fine sieve can be informative. However, some WPPD applications may not be sensitive to such a problem. If only the cell parameters have to be accurately estimated for thermal-expansion studies (Evans et al., 1996[link]), it can be much faster to use WPPD rather than the Rietveld method. However, it is not recommended to do this systematically, especially if the structure is complex and the resolution is low [see the warnings in Peterson (2005[link])].

References

Evans, J. S. O., Mary, T. A., Vogt, T., Subramanian, M. A. & Sleight, A. W. (1996). Negative thermal expansion in ZrW2O8 and HfW2O8. Chem. Mater. 8, 2809–2823.Google Scholar
Peterson, V. K. (2005). Lattice parameter measurement using Le Bail versus structural (Rietveld) refinement: a caution for complex, low symmetry systems. Powder Diffr. 20, 14–17.Google Scholar








































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