I did some tests on the profile of the first diffraction peak of LaB6,
where I added a secondary soller angle, since I used secondary
soller slits, and I added also the parameter for the horizontal
divergence in the equitorial plane. Finally I added a crystallite-size
parameter CS_L. I did the calculation for two measurements: one
with a horizontal divergence of 1/32 degrees and the other with 1/4
degrees. Fundamental parameters were not refined,as it should be.
If the FP description was correct, then CS_L should refine to
approximately the same value in the two cases. Well, it doesn't
(310 and 190 angstrom, respectively). The fits are reasonable, but
not perfect.
Silly question and I think I am missing the point - but how did you fix
the vertical divergence contribution? I thought LaB6 from NIST had a
larger crystallite size than either of your values, suggesting something
has gone wrong in both cases. If the program thinks you have a lot of
sample broadening, when in reality LaB6 was chosen for having very
little, it is probably missing a contribution of the instrument. You
appear to have forced that instrumental thing be Lorentzian by refining
only CS_L. Maybe just refine CS_L and CS_G together? This is unlikely to
solve your problem but remember powder diffraction is only really good
for measuring crystallite size when there is an appreciable size
broadening compared to a line shape standard like LaB6!
And no one has mentioned "tube tails" yet ;-)
Good luck,
Jon
