Hi,

Besides strain and instrument also size broadening can be close to a Gaussian if the crystallite size distribution is very narrow. For zero dispersion of size distribution the size peak profile is about 75% Gaussian and 25% Lorentzian (on tails). For details see JAC (2002) 35, 338-346 (self citation) and other ref. cited there (Langford, Louer, Scardi (2000))

Best,

Nicolae Popa



----- Original Message ----- From: "Leonid Solovyov" <[EMAIL PROTECTED]>
To: <rietveld_l@ill.fr>
Sent: Tuesday, October 21, 2008 10:04 AM
Subject: Re: question on size-strain analysis


Dear Maxim,

Gaussian peak shape is, normally, related to the instrumental, strain and/or lattice distribution broadening. The Williamson-Hall plot shows the dependency of broadening on the diffraction angle and if this dependency can not be explained by strain then it is most probably instrumental. If you use the Bragg-Brentano geometry a possible reason might be a loose powder, sample misalignment or surface roughness.

Regards,
Leonid

*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology  K. Marx av., 42
660049, Krasnoyarsk  Russia
Phone: +7 3912 495663
Fax:    +7 3912 238658
www.icct.ru/eng/content/persons/Sol_LA
*******************************************************

--- On Tue, 10/21/08, Maxim V. Lobanov <[EMAIL PROTECTED]> wrote:

From: Maxim V. Lobanov <[EMAIL PROTECTED]>
Subject: question on size-strain analysis
To: rietveld_l@ill.fr
Cc: "Дмитрий А. Павлов" <[EMAIL PROTECTED]>
Date: Tuesday, October 21, 2008, 7:20 AM
Dear colleagues,

I have a probably very basic question related to
size-strain analysis:

we have a pattern of a nanocrystalline oxide, which shows
(from
Williamson-Hall plot) almost purely size broadening, and
shape of
reflections is to good accuracy Gaussian.
I am curious what type of microstructure this Gaussian
behavior can reflect.
Maybe it is just something usual, but so far I had only
observed
predominantly Lorentzian broadening in similar materials...

Sincerely,
Maxim.


-------------------------------------------
Dr. Maxim Lobanov
R&D Director
Huntsman-NMG
mailto: [EMAIL PROTECTED]

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