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!
Frank
[EMAIL PROTECTED] wrote:
Sorry, pressed the wrong button...
If you just want to try fitting the peaks, you could try something like this:
str
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
sharp
ELSE
broad
ENDIF;
CS_L(csL)
'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
Cheers
Matthew
Matthew Rowles
CSIRO Minerals
Box 312
Clayton South, Victoria
AUSTRALIA 3169
Ph: +61 3 9545 8892
Fax: +61 3 9562 8919 (site)
Email: [EMAIL PROTECTED]
-Original Message-
From: Frank Girgsdies [mailto:[EMAIL PROTECTED]
Sent: Wednesday, 29 October 2008 22:05
To: Rietveld_l@ill.fr
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
b-direction.
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)
--
