Another, related question. 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. If I refine Xe (ptec) in profile function 2 I get a negative value. 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? Which direction is the "broadening axis", how is it defined? By this method, it would seem that I get just two size values, why not three?
Jens > 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? > > Best regards, > > Jens > > 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> > > ------------------------------------------------------- >
