Re: [sdpd] structure and structureless lattice determination

[vanessa peterson <dynoness...@yahoo.com.au>]

>>
I don't know if it is relevant to the discussion, but, the material had
short-range positional disorder.  i.e., the I4/mmm symmetry was broken
locally.

In my investigation I had thought that the difference could be linked to the positional "disorder" of the sample (actually long range ordered disorder - structural modulation). I did not wish to complicate the discussion with this if it was an isolated case. I find the unprompted mentioning of disorder of some interest. 
 
Was this discussed in any resulting publication?
 
Vanessa
 

---------------------------------------------------------

Vanessa K Peterson, 

University of Technology, Sydney

Residing at:

The Bragg Institute, Building 58

Australian Nuclear Science and Technology Organisation

--------------------------------------------------------


Apurva <mehta...@SLAC.Stanford.EDU> wrote:


vanessa peterson wrote:

> Hi all
>
> I'm interested in cell lattice determination using both Le Bail and Rietveld analysis with structure refinement, using the same data. Specifically, where the cell dimensions obtained are not the same.
>
> Has any work been done comparing the lattice dynamics during a structural transition for a sample (such as in situ heating) obtained using a structureless and structure refinement? Such as cell volume during a transition obtained with and without structu
re refinement.
>

I had noticed something similar when refining a K2NIF4 structure
(tetragonal - I4/mmm) from CW neutron data.  The deviation was small,
but significantly larger than the esds.  (LeBail and Rietveld
refinements were done in GSAS.)

(I don't know if it is relevant to the discussion, but, the material had
short-range positional disorder.  i.e., the I4/mmm symmetry was broken
locally.)

************************************************************************
Apurva Mehta
SSRL/SLAC
Bldg. 137, MS 69,  2575 Sand Hill Rd.
Menlo Park, CA 94025-7015
(650) 926 4791, (650) 926 4100 - FAX
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