On 09/05/2014 09:03 AM, Badari Rao wrote:
I have collected EXAFS data on a ferroelectric perovskite Sodium Bismuth
Titanate which has an average rhombohedral R3c structure and am trying
to fit the data with R3c as the starting model. But I am having trouble
in implementing constraints for the fit.
I found a paper authored by you, titled "Local structrue and phase
transitions of BaTiO3, Ferroelectrics, 1998, 206-207, pp 407-430". I
want to do similar kind of analysis using Artemis on my data. However, I
am finding difficulty in understanding how the constraints have been
implemented for the refinement of the barium K edge EXAFS, especially
those for the bond lengths (Page 416 in the above mentioned article in
particular is unclear). Could you please explain how the GDS window and
the variables for different paths in this case would look like. Also how
do you decide what parameters to refine and what to keep fixed (table IV
in the article)?
Also can you please suggest some literature for beginners which can
guide me in implementing such constraints?
Badari,
You are asking a very broad and open ended question. Since you
self-identify as a beginner, I would recommend spending some time
learning the basics of XAS and XAS analysis. You could start by
reading one of the recent text books on XAS by Grant Bunker or Scott
Calvin:
http://www.amazon.com/Introduction-XAFS-Practical-Absorption-Spectroscopy/dp/052176775X
http://www.amazon.com/XAFS-Everyone-Scott-Calvin/dp/1439878633
To learn about the practice of XAS, there are links to tutorials at
http://xafs.org/Tutorials
Shelly Kelly's tutorials specifically address the use of Athena and
Artemis.
To learn about the use of my software, there are links to a lot of
information, including links to videos of me demonstrating their use,
at the Demeter website:
http://bruceravel.github.io/demeter/
To learn specifically about the application of constraints to EXAFS
analysis, two excellent papers with extensive discussions of how to
apply sophisticated constraints are:
http://dx.doi.org/10.1103/PhysRevB.66.224405
http://dx.doi.org/10.1016/S0016-7037(02)00947-X
While neither of those papers are on the topic of titanate
perovskites, you would do well to read them carefully and understand
the analysis strategies that Scott or Shelly describe.
HTH,
B
--
Bruce Ravel ------------------------------------ bra...@bnl.gov
National Institute of Standards and Technology
Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
Building 535A
Upton NY, 11973
Homepage: http://bruceravel.github.io/home/
Software: https://github.com/bruceravel
Demeter: http://bruceravel.github.io/demeter/
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