To all:
Initially I sent this to Alan who suggested I open discussion to the entire
community. I've posted similar in past years and have been FLAMED. Please
keep it civil. ;-)
=
As a long time practitioner of powder XRD (since 1972) I was there when the
superconductor
To all:
I have electronic grade silicon wafers (6-9s pure) which I'm willing to share.
They are not certified by NIST. They are from silicon single crystal
production and are many years old. You can grind and mix with your material of
interest and use the line positions to ascertain peak
To All:
RE: X-RAY DIFFRACTION PROCEDURES ... SECOND EDITION, Klug Alexander, Table
9-2, p. 659.
According to this reference, the relative breadth of a peak in the powder
diffraction pattern is related to that of every other peak. The relationship
is according to the shape of the crystal.
Back to basics and First Principles
As Alan says, the [use of the Cagliotti function is appropriate for the neutron
case], but not really for X-ray and other geometries.
My recollection is the Cagliotti function was adapted to the x-ray case when we
had low resolution x-ray instruments
Back to basics. Caglioti Function is instrument function and is often times
used inappropriately.
Just my two cents worth (and these days, 2-cents ain't worth much...)
Frank May
St. Louis, Missouri U.S.A.
From: Jon Wright [mailto:wri...@esrf.fr]
Sent:
To all:
What is the correct procedure for refining U,V,W? It is my understanding that
those parameters are a function of instrument geometry. Does one use a
standard material to determine U,V,W and then fix their values for the
instrument you're using?or do the values of U,V,W change
You can check for texture effects (preferred orientation) by obtaining multiple
patterns of the material. It's realistic to expect some differences, but
preferred orientation is manifest by not being able to replicate the pattern.
That's the simple test. Let us know what you find.
Another
To all:
The mathematical description of crystals is valid for the bulk of the volume.
However, the description suffers from a physical termination of series
effect at the surface of the crystal. For very large crystals, the amount of
surface is much greater relative to the total volume of
Regarding Crystallinity -
As a technicality, the concept of % crystallinity is not only an x-ray
analysis issue. One can measure % crystallinity by other methods - and the
findings (numbers) from the different techniques are not necessarily the same.
I'm not sure if there is a technique
As Pamela Whitfield indicates below, this is not a straightforward issue.
Reading the reference in Dr. DM's posting, one see that it is necessary to have
100% crystalline or 100% amorphous or 50% crystalline/50% amorphous
standards. The rub is that it is necessary to have a means to determine
I've watched this thread develop over the past few days. Apparently there is
little advice forthcoming about the original inquiry.
Just one person's observation.
Frank May - University of Missouri-St. Louis
winmail.dat
Peter et al.,
If the reason for their use is historic and somewhat convenient, but their
usual application is based on no theory whatsoever, why does their use
continue?
It is generally recognized that adding parameters to a least squares fitting
process causes refinement to proceed to a
To all:
OBSERVATION: Most of the reported X-ray Rietveld analyses I've seen include
refined values for U, V, W which are dependent on the particular sample of
interest.
As you say below regarding U, V, W: They can be a bit hard to determine
unless a very high quality pattern is used for
If you've eliminated the possibility of target or sample impurities, the
so-called Renninger Reflections would also be my guess. However, I also don't
have the (picture of) data to observe.
If the continuous ring [re: Andrew Payzant below] refers to a transmission
photo of a powder, then
With regard to constrained refinement: Should one first refine lattice
parameters and then fix them before proceeding with structure refinement? As
I see it, lattice parameters are directly observable in the xrd pattern; if one
allows lattice parameters to change during structure refinement,
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