Negative U's in Rietveld can arise from several causes, so that there is
not one single answer. Some of the reasons are
1. The structural model is simply incorrect.
2. High absorption means that the low-angle data are weaker than they
should be, or conversely that the high-angle data appear
Kurt
The standard method is to use a wavelength made from the weighted (2:1) average
of the two components. So for CuKa the standard value is 1.5418 angstroms
Mike Glazer
-Original Message-
From: Kurt Leinenweber [mailto:ku...@asu.edu]
Sent: 15 January 2010 16:46
To: Franz Werner;
As I have said before countless time, one should not lose sight of the
objective of Rietveld refinement, that it is to refine a sensible
crystallographic structure. One can reduce R factors in all sorts of
ways by playing with the peak shape functions (even by using lower
symmetry and increasing
Alan
I think you are misunderstanding what the PDF method is used for. The
idea is to fourier transform directly the whole range of scattering
including peaks and background (after removing artifacts in the
background due to the diffractometer, air scattering etc). In a highly
ordered crystal
Determination of crystallinity can be a fraught subject, because it is
usually assumed in such measurements that the background is from
amorphous material while the sharp peaks are from crystalline material.
So the standard way to do this would be to have a method for extracting
the background and
As I have said in reply to Leonid, I don't know why we have such a large
difference in our experimental setup. It may be that our 0.02 slits are
misaligned -- I will have to check this.
The question of what is meant by signal to noise ratio in connection with
powder diffraction is one which I
Leonid
I don't know why we have such a large difference, but for some reason we
do. I will send you privately the two diagrams.
Mike
-Original Message-
From: Leonid Solovyov [mailto:[EMAIL PROTECTED]
Sent: 19 February 2008 03:56
To: rietveld_l@ill.fr
Subject: RE: advice on new powder
Alan
I absolutely agree with you regarding Rietveld refinement. The same
argument is true for adjusting peak shapes to get the best fit, playing
around with different peak formulae. Often such tweaking, while it makes
the observed and calculated fit look nicer, has little effect on the
atomic
How do you define signal to noise in powder diffraction? I have seen this term
used several times, but I have not found a definition so far with regard to
powder diffraction per se.
I have just done two runs on a Panalytical one with 0.04 soller slits and one
with 0.02 (both with a CuKa1
Yes it does. One way is to add the command adps at the end of the line
site E.g.
site Pb1x 0.23y 0.15 z 0.28 occ Pb 1 adps
Mike Glazer
-Original Message-
From: Peter Tzvetkov [mailto:[EMAIL PROTECTED]
Sent: 10 December 2007 18:28
To: rietveld_l@ill.fr
Subject: Topas
Dear
There is an old method that I used to use for capillaries that you may
useful. Take a metal wire of appropriate diameter and dip it into
collodion (nitrocellulose dissolved in acetone), allow it to dry. Then
stretch the wire with pliers and slip off the cellulose capillary. This
is cheap, quick,
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