Hello everybody,
i have a question about the GSAS software. Indeed, i would like to know
what are exactly the L11, L22, L33L23 parameters. I saw that these
parameters represent the anisotropic microstrain in material. Moreover,
there is an empirical _expression_ which uses these parameters as
At least, in the classical article by Peter Stephens (J. Appl. Cryst., 32,
281) it is written about this and similar approaches that "these methods
have been successful in producing improved line-shape fits, even though no
theoretical justification or microscopic model has been given".
The descrip
>From my experience both functions #3 and #4 work fine when broadening anisotropy is
>not significant.
I found #4 more works better when anisotropy is large (up to 2 times); in this case
improvement is substantial
Peter Zavalij
-Original Message-
From: Maxim V. Lobanov [mailto:[EMAIL P
Popa
- Original Message -
From:
Christophe Chabanier
To: [EMAIL PROTECTED]
Sent: Wednesday, April 07, 2004 6:45
PM
Subject: GSAS informations
Hello everybody,i have a question about the GSAS
software. Indeed, i would like to know what are exactly the L11, L22,
L33..
Hi,
>The coefficients Lij in the formula you wrote have no significance.
Our whole science is a so bad approximation to the Universe...
For the representation of an isotropic size effect , you may imagine
the mean size being the same in all directions, obtaining a
sphere. The same for a mean str
> Our whole science is a so bad approximation to the Universe...
>
> For the representation of an isotropic size effect , you may imagine
> the mean size being the same in all directions, obtaining a
> sphere. The same for a mean strain value.
>
> Introducing some anisotropy in mean size and mean
To a happy Easter,
It seems that we disagree on the meaning of some
english words. English is not my mother language, so I may be
wrong.
The naive character doesn't come from the approximation of the crystallite
shape by an ellipsoid, but from the approximation of the size effect in
powder diffr
Nicolae Popa wrote:
the condition to not violate some elementary principles, in particular,
here, the invariance to symmetry.
Dear Prof Popa,
I had been meaning to implement the quartic form for peak width in a
refinement program for some time, but did not figure out how to generate
the const
Hi,
> It seems that we disagree on the meaning of some
> english words. English is not my mother language, so I may be
> wrong.
Nor mine, so I can be equally wrong (or worse).
> I was able to put one word on that definition (thanks for it) in my
> previous email : distribution (a size distributi
Presume one of your students makes a fit on a sample having only size
anisotropy and he is able to determine the six parameters of the ellipsoid.
But after that he has a funny idea to repeat the fit changing (hkl) into
equivalents (h'k'l'). He has a chance to obtain once again a good fit, with
oth
>
> >Presume one of your students makes a fit on a sample having only size
> >anisotropy and he is able to determine the six parameters of the
ellipsoid.
> >But after that he has a funny idea to repeat the fit changing (hkl) into
> >equivalents (h'k'l'). He has a chance to obtain once again a go
He could ask the master how is the nature so perfect.
Or could conclude by himself that powders are not single
crystals, so that symmetry may lead to systematic overlap
and irrecoverable loss of information.
Yes, anisotropic line broadening is rarely observed
with cubic compounds unless in very sp
I just wanted to add my 2 cents to this argument...
I think one big point in all the discussion on size and strain concerns
the difference between what IS in the specimen, what we see with our
probe (X-rays or neutrons, presumably) and what we reconstruct using A
model. In most cases the model
> Not violating symmetry restrictions you may either
> have the sphere with the terms 11=22=33 and 12=13=23=0
> or something else allowing the 12=13=23 terms to be equal
> but different from 0. These two possibilities are all you can do
> in cubic symmetry with h,k,l permutable. If I am not wrong.
Not violating symmetry restrictions you may either
have the sphere with the terms 11=22=33 and 12=13=23=0
or something else allowing the 12=13=23 terms to be equal
but different from 0. These two possibilities are all you can do
in cubic symmetry with h,k,l permutable. If I am not wrong.
The (111)
(you could be a good boxeur, Armel!),
Knocked out at round 4 ! Argh !
Anyway, a sphere was good enough for the previous
size-strain round robin... Hope that the next size-strain
round robin will be more complex, and will succeed
in excluding definitely any ellipsoid from the ring.
Armel
>
> >(you could be a good boxeur, Armel!),
>
> Knocked out at round 4 ! Argh !
Some people believe that "fair play" is mainly an Anglo-Saxon apanage
(prerogative). Obviously they are wrong.
>
> Anyway, a sphere was good enough for the previous
> size-strain round robin... Hope that the next siz
> Dear Prof Popa,
>
> I had been meaning to implement the quartic form for peak width in a
> refinement program for some time, but did not figure out how to generate
> the constraints from a general list of symmetry operators. Is there a
> simple trick for doing this? I was thinking of just choosi
>... to answer to your (too) long questions. May be later, OK?
Going back to this quartics versus ellipsoids peak broadening stuff,
maybe I can summarise:
Why should the distribution of lattice parameters (=strain) in a sample
match the crystallographic symmetry? If the sample has random, isolat
Dear Jon,
Jon Wright wrote:
>... to answer to your (too) long questions. May be later, OK?
Going back to this quartics versus ellipsoids peak broadening stuff,
maybe I can summarise:
Why should the distribution of lattice parameters (=strain) in a
sample match the crystallographic symmetry? If t
Jon,
I risk a public reply here. One possibility everyone should be open to is that a real
phase change has occured during some experimental manipulation of your sample. Some
phase changes are quite subtle and involve only slight (and at first sight) quite odd
line broadening. Higher resolution
Dear Bob and Jon,
one reply from the public is: come to share your and to get other ideas
to the meeting Size-Strain IV (http://www.xray.cz/s-s4/), a satelite
workshop of the EPDIC-9 (http://www.xray.cz/epdic/), end of this summer
in Prague.
The thinks can be even more complex: The supperpositi
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