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 shi
Greetings from HOT St. Louis, MO.
I find it silly to discuss inclusion of a 64K image in email. In the early
days (1970s) of useful scientific computing, we said, "core [memory/computing
space] is gold;" we wrote our own programs; large programs were 50K. We have
made progress. Our computers
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 cr
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 refinemen
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 i
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 fo
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 l
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
<>
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 dete
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 o
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 i
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 dep
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: T
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
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.
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