Dear All:
Indeed, despite some more advanced approaches to modeling diffraction line
shapes, the good, old Cagliotti function is still in use probably for
historical reasons (as it is the case with many other things in sciences).
However, to be fair to (practically all major) Rietveld programs, th
As Maxim says, strain-related parameters are U and Y. By the same token,
size-related parameters are P and X (both go with 1/cos(Theta). The reason is
that this Rietveld model (the so-called TCH) assumes a Voigt function for both
size and strain profile and therefore has to have both Lorentzian
Stefan:
The recent paper (Journal of Applied Crystallography 37 (2004) 911-924)
gives several recommendations and recipes for extracting size/strain
results, using Rietveld refinement, in particular GSAS. The reprint can be
downloaded from http://www.du.edu/~balzar/
Good luck,
Davor
> -Orig
It was shown in paragraph 6 of JAC 35 (2002) 338-346 that size-broadened
profiles given by both lognormal and gamma distributions can be approximated
by a weighted sum of Lorentz and Gauss functions for a broad range of
distribution dispersions. Besides, round robins can sometimes be long
adventure
I guess, this discussion has already died down but I couldn't find a moment for
reply soon enough:-)
As Prague was already mentioned, let me try to summarize what I think about
this subject and have said there (let's hope I actually remember it:-):
1. A careful line broadening analysis (at this
gt; Sent: Sunday, March 27, 2005 12:49 AM
> To: rietveld_l@ill.fr
> Subject: RE: Size Strain In GSAS
>
> On Friday 03/25 Davor Balzar wrote:
> > Paragraph 3.3 of the article that you mentioned explains how were
> >size and strain values calculated. One can even obtain si
size and
strain values calculated. One can even obtain size distribution by following
the procedure that was posted to this mailing list several months ago; see
below.
Best wishes,
Davor
Davor Balzar
Department of Physics & Astronomy
University of Denver
21
if the
size distribution is narrow.
Davor
****
Davor Balzar
Department of Physics & Astronomy
University of Denver
2112 E Wesley Ave
Denver, CO 80208
Phone: 303-871-2137
Fax: 303-871-4405
Web: www.du.edu/~balzar
***
ext Round Robin steps could benefit from an open discussion
> here, and viewpoint exchanges. This is not time lost (I hope).
I agree.
>
> Have a nice week-end,
You too, and keep an eye on those 300 g of powder. We'll probably need it:-)
Davor Balzar
good case in the
paper why we believe the sample was strain-free.
In view of this, I hope that you'll indeed be the referee or it might get
rejected:-) But, regardless of who the referees are, we could have used some
of this time to work on the manuscript instead:-)
Best regards,
Davor
hich would tend to be
overestimated in a cluttered pattern and consequently systematically
affecting both size and strain values.
Davor Balzar
his justifies why we tried to have
measurements collected on different instruments in the round robin, although
it might have been a problem for some participants.
Best regards,
Davor Balzar
**
National Institute of Standards and Technology
Materia
> >Yes, it was done (see J. Appl. Cryst. 26 (1993) 97-103) and the
> >column-length distribution function appears to have an "acceptable"
> >asymmetric shape for tested samples.
>
> You mean that whatever a Voigt function, it corresponds to a
> reasonable size distribution function ? This is hard
>
> >Very often, a simple assumption that
> >size-broadened profile has both Lorentzian and Gaussian terms yields
> >satisfactory results.
>
> Well, this assumption is easily entered in a pseudo-Voigtian or Voigtian
> profile shape model. But the corresponding size Fourier coefficients
> AnS are
Dear Armel:
Although I sent the message unintentionally to the whole list, why not have
a public discussion.
> including Gaussian. But the size model is currently only
> Lorentzian in ARIT. There is no way to have a pure Gaussian
> shape for the size effect since it corresponds to unphysical
> s
Hi Armel:
I am impressed -- nice report:-)
One comment regarding ARIT. I didn't go carefully through all the results
but my impression is your values are a bit underestimated. If you added
additional Gaussian term to your An, you should get results much closer to
WA. That should be relatively si
ar/ or from the European CCP14 mirror
at the http://www.ccp14.ac.uk/ccp/web-mirrors/balzar/div853/balzar/
The deadline for returning the results to the Round-Robin organizer is set
for October 20, 2000!
Your participation is greatly appreciated
ar/ or from the European CCP14 mirror
at the http://www.ccp14.ac.uk/ccp/web-mirrors/balzar/div853/balzar/
The deadline for returning the results to the Round-Robin organizer is set
for October 20, 2000!
Your participation is greatly appreciated
A PDF reprint can be found at
http://www.boulder.nist.gov/div853/balzar/PRB03414.pdf
As for the Eui-Suk's question, a good starting point to understand the
BaTiO3 structure and other properties is the book of Jona and Shirane,
Ferroelectric Crystals, Pergamon Press.
Regards,
Da
can be found at the following Web site:
http://www.nist.gov/oiaa/pdfront.htm.
Before submitting the applications, prospective candidates should contact:
Dale W. Fitting 303-497-3445[EMAIL PROTECTED]
or
Davor Balzar303-497-3006[EMAIL PROTECTED]
the CCP14 site:
http://www.ccp14.ac.uk/ccp/web-mirrors/balzar/div853/balzar/s-s_rr.htm
You participation and help are greatly appreciated.
The Organizer,
Davor Balzar
**
NIST
Materials Science and Engineering Laboratory
Div. 853, 325 Broadway
Bo
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