Hello everyone, I fear my last mails to the list got lost in an ILL server breakdown, so I'll try again:
I have some material with nanometer sized Cu crystallites that show anisotropic line broadening. Depending on preparation the 200 integral breadth is 40-60 % larger than 111 integral breadth. Intuitively, I do not expect such an effect from size anisotropy in a cubic material because of the high symmetry, but reading up on litterature and old Rietveld list posts makes me less confident and more confused. I would like to understand exactly how the line widths are calculated for a given shape of crystallites. Reading Langford & Wilson (1978), JAC 11, 102-113 and Langford & Louer (1982), JAC 15, 20-26, I don't understand how multiplicity is handled and what the effect is of shape with respect to the crystallographic orientations. I suspect that the broadening may be caused by stacking faults or twinning, but how do I determine whether this is the case? If I do a Rietveld refinement of this material, it IS possible to get a good fit by refining an anisotropic size broadening component in GSAS. When I look in the manual, it states that I can get the anisotropic size components from Lx and Xe in the direction along the "broadening axis" and perpendicular to it. What does that mean? I found out how to define the broadening axis, but if I specify e.g. the 100 direction, what is then the physical meaning of this? It is entirely possible to set the Xe value to some arbitrarily large number, which makes the 200 reflection infinitely broad, while leaving the 111 reflection unaffected. To me, this does not make sense. Some guidance will be much appreciated. Best regards, ph.d. student Jens Wenzel Andreasen Risoe National Laboratory Frederiksborgvej 399 DK-4000 Roskilde Denmark Phone: +45 4677 4720 Fax: +45 4677 5758 ------------------------------------------------------- If your messages to me are rejected take a look at: <http://www.risoe.dk/ita/email/liam_uk.htm> -------------------------------------------------------
