Hi Juro, I had some fun playing with this project file. I hope you don't mind. Here is a list of suggestions. 1st: Don't use the paths that are less than 0.1 Angstroms apart. 1st-b: If you don't know the CN set it to ONE and then vary just the amplitude. There is a degen box multiplied by a amp box. Degen should be one. 2st: set the values for CN, and s2, while letting delr vary 3rd. Let the CN and delr vary. You will find that the Fe path around 3 Ansgroms isn't needed. 4th. Make sure your fit range and data ranges are appropriate. 5th. Add as much constraints as you think is reasonable. First Oxygen coordination number should be 6 or 4 total. I thought 6 worked well. 6th. Fit the data with k-weight of 1,2, and 3, to get the uncertainties smaller. Take a look at the project file. I think that this model or one like it might work. You need a separate S02 value from the Amp value. Amp should be S02*Amp. I didn't add a S02 part. You should get that from a known standard measured on the same beamline. S02 should be between 0.70 and 1.0. So the CN reported are likely a bit too big. Good luck, Shelly Shelly Kelly Bldg 203 RM E113 Skelly@anl.gov Argonne National Laboratory 630-252-7376 9700 S Cass Ave www.mesg.anl.gov Argonne, IL 60440
-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit- bounces@millenia.cars.aps.anl.gov] On Behalf Of Juraj Majzlan Sent: Monday, September 26, 2005 8:46 AM To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Fe oxide
Hello,
I am trying to fit an EXAFS spectrum of an X-ray amorphous Fe precipitate. In a model (goethite), there are Fe atoms at 3.02, 3.29, and 3.45 A. Fitting the two most distant shells of iron gives strange results. Fitting them simultaneously gives very high amplitudes (32, -66) which cancel each other (fig. 1) and produce a beautiful and unreasonable fit (fig. 2).
Fitting them separate gives small ('reasonable') amplitudes, but the distance (dr) have very high uncertainties, e.g., dr = 0.12 +- 20.3.
Can I expect to resolve these three Fe shells or is it asking too much?
I am also attaching the Artemis file, but will appreciate any comments and suggestions.
Juro Majzlan
---------------------------------- Juraj Majzlan Institute of Mineralogy and Petrology Albert-Ludwig-University of Freiburg Albertstrasse 23b Freiburg, D-79104, Germany telephone +49-761-203-6416 fax +49-761-203-6407 http://www.minpet.uni-freiburg.de/sites/personen/majzlan.html