Re: Quantitative analysis

2008-10-29 Thread Radovan Cerny


Hi Blaise
In Bragg-Brentano mode, sample spinning does nothin for PO. This is 
because the diffraction vector is normal to the sample surface, and 
sample spinning rotates along this vector.

That's wrong! As I have already written, the empirical PO corrections 
like March-Dollase and Rietveld-Toraya suppose that the PO is fibre-like 
(axial symmetry). If your sample does not have fibre-like PO, you can 
create it by sample spinning.


Spinning does increase your particle statistics, which almost always helps.
If you're looking at a capillary, spinning the capillary does help with 
PO, but just being in a capillary helps PO.
As to spinning speeds, a good guide is one revolution per data point.



Matthew Rowles

CSIRO Minerals
Box 312
Clayton South, Victoria

Ph: +61 3 9545 8892
Fax: +61 3 9562 8919 (site)

Radovan Cerny
Laboratoire de Cristallographie
24, quai Ernest-Ansermet
CH-1211 Geneva 4, Switzerland
Phone  : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08

RE: Quantitative analysis

2008-10-29 Thread Daniel Chateigner
hi all,

not only fibre like, but single component fibre, and with the fibre axis
parrallel to the sample normal (i.e. cyclic fibre. this is very
restrictive and generally does not correspond to the real texture.
Contrarilly to what has been said here or there, the March-Dollase does
not ensure PO normalisation, but only the normalisation of this single
component, there is then no physical restriction between all hkl lines in
terms of crystal angles, which gives rise to a lot of fitting space with
unreasonable solutions either in terms of QTA or QPA.
A physically based correction for PO needs the calculation of the ODF, and
more than a single pattern to be measured. But this is the price to pay
for a corect estimate of phase amounts in textured samples.


Daniel Chateigner
Bd. M. Juin
14050 Caen, France

RIET: availability of Golden Book of Phase Transitions, Wroclaw (2002)

2008-10-29 Thread Lachlan Cranswick

A quick query for people

A few of the ICSD crystal structure entries (such as  [Metathenardite] 
Disodium sulfate(VI)) have references to:

  Golden Book of Phase Transitions, Wroclaw (2002)

Does anyone know if this book really exists and where it can be
obtained from?  Even  does not seem to 
know about it.

Thanks in advance,


Lachlan M. D. Cranswick
Contact outside working hours /
  Coordonnees en dehors des heures de travail:
NEW E-mail / courriel:  lachlanc *at*
Home Tel: (613) 584-4226 ; Cell/mobile: (613) 401-6254
P.O. Box 2057, Deep River, Ontario, Canada, K0J 1P0

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RE: Anisotropic peak broadening with TOPAS

2008-10-29 Thread Matthew.Rowles
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)