Hi to all!,
in fact, the Cagliti's expression is just a way to show the angular
variation of fwhm, as was mentioned was usef for neutron diffraction and
adopted in XRD, we can also build another dependence such as FWMH vs
2theta directly and it is useful to evaluate size and strain, the problem
i
. Many times one can reduce R factors
by playing with the diffraction geometry terms, but with little obvious
improvement of the structural results.
-Original Message-
From: Alan Hewat [mailto:he...@ill.fr]
Sent: 20 March 2009 07:13
To: rietveld_l@ill.fr
Subject: RE: UVW - how to avoid
matthew.row...@csiro.au said:
> From what I've read of Cagliotti's paper, the V term should always be
> negative; or am I reading it wrong?
That's right. If
FWHM^2 = U.tan^2(T) + V.tan(T) + W
then the W term is just the Full Width at Half-Maximum (FWHM) squared at
zero scattering angle (2T). FWHM^
>From what I've read of Cagliotti's paper, the V term should always be
>negative; or am I reading it wrong?
Additionally, there is some good work on the use of the Cagliotti (and TCHZ)
functions in the paper by Young and Desai; it also goes over how to incorporate
sample dependent terms into th
)^2 + v0 *tan(theta) + (w0 + s^2) where
e^2 = f^2-s^2 - and we've got the Gaussian component of the size and
strain directly from the Cagliotti relationship.
-Original Message-
From: Jon Wright [mailto:wri...@esrf.fr]
Sent: 19 March 2009 20:49
To: alan.he...@neutronoptics.com
Alan Hewat wrote:
Jon Wright said:
Quick question - does anyone have a trick to stop the Cagliotti formula
going negative?
This can happen if the resolution is relatively flat, so that there is no
well defined minimum.
Seems to be the problem - also rather close to zero anyway.
if yo
Jon Wright said:
> Quick question - does anyone have a trick to stop the Cagliotti formula
> going negative?
This can happen if the resolution is relatively flat, so that there is no
well defined minimum. Then the quadratic Cagliotti formula produces large
correlations between U,V,W. The trick is
Sent: Thu 3/19/2009 8:58 AM
Cc: Rietveld Method
Subject: Re: UVW - how to avoid negative widths?
> According to Caglioti relation, the dimensions of U,V,W are as (angle)^2.
Quick question - does anyone have a trick to stop the Cagliotti formula
going negative? Prodd currently has a habit of
According to Caglioti relation, the dimensions of U,V,W are as (angle)^2.
Quick question - does anyone have a trick to stop the Cagliotti formula
going negative? Prodd currently has a habit of bugging out on a
sqrt(negative) and I'm wondering how other folks worked around that, or
if I've go
