On Monday 28 May 2007, Joji Kuniya wrote:

I analyzed EXAFS spectra of trace of Fe in lithium tantalate crystals. At first, I created the feff.inp file of LiTaO3. Then I changed central Li atom to Fe atom and added Fe atom at the Ta site. So that, the fitted results is good except amp(amp results is 0.3). I think that the model structure is good, but I can not understand why amp is too low. How do you think about this results? And, I tried to fitting treatment using GDS parameters. But, I do not know that the general method how to use the GDS parameters. Please tell me the general way of GDS manipulation. My PC runs under Win XP, and My Artemis runs under feff8 conditions. Thank you. Joji Kuniya

Hi Joji, You don't really provide enough information to give a good answer to your questions. I suspect that your problem has something to do with the fact that the amplitude and the various sigma^2 values are highly correlated. Without more information about how you are actually parameterizing your fits, though, it is hard to comment on that value of amp. I am confused that you put Fe on both the Li and Ta sites. Is that actually reasonable? Could be -- but my hunch is that Fe would prefer to sit on the Ta site. Having the wrong element on a site can do bad things to a fit. If you haven't done so already, I would recommend that you work through Scott Calvin's ZnO example, which you can find at: http://cars9.uchicago.edu/iffwiki/HoraeSoftware#contrib It is a very nice introduction to Ifeffit and Artemis and to the Ifeffit way of thinking about exafs analysis problems. B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advance Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/

Thank you so much for many experts replay. Lithium tantalate crystal is R3c space group and actually have many hole at Li site . I think that Fe should be replaced to Li or implemented to the absent site. At first, I made the structure which was exchanged Li to Fe, but this structure was not fitted to the data. So that , I changed z value of Li of atoms on the input data to smaller and changed Li to Fe. I used default GDS parameters for the fitting because my knowledge of how-to manipulating GDS is not enough. I used 6 paths for the fitting. 1-3.4(1/k) range and kw=1 was used. Should I think about all paths? (Feff calculation makes 170paths). I received ZnO tutorial file from Dr.Fons last month. I studied the tutorials two or three times, but I could only have little knowledge what the meanings of the GDS parameter manipulations, because of my little knowledge of XAFS principals. I will read some XAFS tutorials. And, I will try some other structures and try more paths in fittings. Thank you. ----- Original Message ----- From: Joji Kuniya To: ifeffit@millenia.cars.aps.anl.gov Sent: Monday, May 28, 2007 7:51 PM Subject: [Ifeffit] Low amp results I analyzed EXAFS spectra of trace of Fe in lithium tantalate crystals. At first, I created the feff.inp file of LiTaO3. Then I changed central Li atom to Fe atom and added Fe atom at the Ta site. So that, the fitted results is good except amp(amp results is 0.3). I think that the model structure is good, but I can not understand why amp is too low. How do you think about this results? And, I tried to fitting treatment using GDS parameters. But, I do not know that the general method how to use the GDS parameters. Please tell me the general way of GDS manipulation. My PC runs under Win XP, and My Artemis runs under feff8 conditions. Thank you. Joji Kuniya ------------------------------------------------------------------------------ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit