Dear Matthew,

thanks for your reply.
I hope to look a bit deeper into it (and try the code)
a little later today.
At the first glance, however, I'm not sure whether
treating hk0 and hkl the same way would be appropriate
from the theoretical point of view.
But as I'm a practical guy, I will just give it a try.

Thanks again!

Sorry, pressed the wrong button...

If you just want to try fitting the peaks, you could try something like this:

        phase_name "Metal_oxide"
        local broad 100 'crys size for hk0 and hkl
        local sharp 2000 'crys size for 00l
        local csL =
                IF (And(H == 0, K == 0, L > 0)) THEN

        'insert remainder of structure...

I don't know much about Lvol, but isn't an "average" crystallite size for a 
highly asymmetric crystal not all that meaningful? I am willing to be educated here, as I 
haven't had much need to get accurate crystallite size from diffraction data before....



Matthew Rowles

CSIRO Minerals
Box 312
Clayton South, Victoria

Ph: +61 3 9545 8892
Fax: +61 3 9562 8919 (site)
-----Original Message-----
From: Frank Girgsdies [mailto:[EMAIL PROTECTED]
Sent: Wednesday, 29 October 2008 22:05
Subject: Anisotropic peak broadening with TOPAS

Dear Topas experts,
C) One could leave the spherical harmonics approach
and go to a user defined model, which refines different
Cry Size parameters for different crystal directions.
In my case, two parameters would probably be sufficient,
one for the c-direction, and a common one for the a- and
The Topas Technical Reference, section 7.6.3. gives a
similar example of a user defined peak broadening function,
depending on the value of l in hkl.
I could probably come up with an analogous solution
which has a 1/cos(theta) dependence and two parameters,
one for the 00l and one for the hk0 case.
My problem with this approach is how to treat the
mixed reflections hkl. I suppose they should be
scaled with a somehow weighted mix of the two
parameters, where the weighting depends on the
angle between the specific hkl and the c-axis.
However, I no idea how a physically reasonable
weighting scheme (and the corresponding Topas syntax)
should look like.
Frank Girgsdies
Department of Inorganic Chemistry
Fritz Haber Institute (Max Planck Society)

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