Re: [Ifeffit] Amorphous
On 08/08/2016 11:19 AM, Carlos Triana Estupinan wrote: I want to know if it is possible to obtain a 3D structure (.cif file) of an amorphous material from the EXAFS fitting carried out from artemis. I mean, there is a way to extract a .cif file with the structural data obtained from the refined spectra. No. EXAFS is basically a one-dimensional measurement. You measure R. Multiple scattering gives you limited information about the 3D arrangement of atoms, but mostly EXAFS is just R. Unless I am misunderstanding the question, I don't think you can do what you are asking even for a well-ordered crystal, much less an amorphous material. Also, in amorphous materials there must be a distribution of interatomic bond distances and coordination, and so, how can I address such a structural distribitions. Well, sure. There is a while literature on the use X-ray or neutron scattering along with EXAFS and molecular dynamics and monte carlo methods to study amorphous materials. It seems that the most successful approaches involve forward modeling -- i.e. testing structures against the EXAFS data. There simply isn't enough information in EXAFS to invert the EXAFS and extract a 3d configuration. Artemis does not even try to do that. B -- Bruce Ravel bra...@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS-II Building 743, Room 114 Upton NY, 11973 Homepage:http://bruceravel.github.io/home/ Software:https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/ ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
[Ifeffit] Amorphous
Dear Bruce I want to know if it is possible to obtain a 3D structure (.cif file) of an amorphous material from the EXAFS fitting carried out from artemis. I mean, there is a way to extract a .cif file with the structural data obtained from the refined spectra. Also, in amorphous materials there must be a distribution of interatomic bond distances and coordination, and so, how can I address such a structural distribitions. Regards. ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit
Re: [Ifeffit] amorphous metal alloys EXAFS spectra to be fitted with Artemis
Hi Piotr, Matt wrote everything, but I have 2 small comments: - Fe environment if it is oxide or metallic state can be visible directly from the distance in most cases. - Piotr, you wrote nothing about composition (and detection method and preparation of the sample for the experiment) - only that you have 6 additional elements, what is stoichiometry and what kind of elements? This information can decrease the number of input parameters... Giving you advise knowing nothing about your sample is as a guesswork... Regards kicaj W dniu 13-08-24 23:18, Piotr J. Bardziński pisze: Dear Sir or Madam, I got a normalized Fe K-edge EXAFS spectrum for my amorphous 7-component alloy sample, for which I know its atomic percent composition. I need to find out the interatomic distances between the Fe and the other atoms present in the alloy (identify the peaks in R-space) as well as how many atoms of each element is surrounding the absorbing iron atom (coordination number). To meet my goal, I think I need to fit the R-space Fourier transform of my EXAFS spectrum in a program like Artemis. Unfortunately, I haven`t found any tutorial discussing how to deal with amorphous sample with unknown organization of the atoms. When you are about to prepare an atomic model in Artemis for fitting, you need to build a model with an initial interatomic distances, atomic coordination number, etc, but all that is obviously unknown to me. I know nothing about the short range order in my material and I want to learn it from the experiment itself (note that itcan be and most probably is different from the one present in crystalline structures). So, my question is, could somebody tell me how to deal with such system using the Artemis, what type of initial models for fitting should be prepared? All of your help will be greatly appreciated. Best regards, Piotr Bardziński, ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Re: [Ifeffit] amorphous metal alloys EXAFS spectra to be fitted with Artemis
Hi Piotr, On Aug 24, 2013 4:19 PM, Piotr J. Bardziński bardzin...@poczta.fm wrote: Dear Sir or Madam, I got a normalized Fe K-edge EXAFS spectrum for my amorphous 7-component alloy sample, for which I know its atomic percent composition. I need to find out the interatomic distances between the Fe and the other atoms present in the alloy (identify the peaks in R-space) as well as how many atoms of each element is surrounding the absorbing iron atom (coordination number). To meet my goal, I think I need to fit the R-space Fourier transform of my EXAFS spectrum in a program like Artemis. Unfortunately, I haven`t found any tutorial discussing how to deal with amorphous sample with unknown organization of the atoms. When you are about to prepare an atomic model in Artemis for fitting, you need to build a model with an initial interatomic distances, atomic coordination number, etc, but all that is obviously unknown to me. I know nothing about the short range order in my material and I want to learn it from the experiment itself (note that it can be and most probably is different from the one present in crystalline structures). So, my question is, could somebody tell me how to deal with such system using the Artemis, what type of initial models for fitting should be prepared? All of your help will be greatly appreciated. Best regards, Piotr Bardziński, ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit If you really know nothing about the local structure around iron, you might be in for a challenging introduction to EXAFS analysis. You might actually have some idea about the local structure from the XANES, say for example if the iron is oxidized or is it still really in a metallic state. Even if only that, it is a place to start For EXAFS with artemis, you'll want to start with guesses of the local environment. They don't need to be good guesses, a suitable crystal structure will do, and you really only need to get the first shell distances close, because you'll refine these distances. You will probably need to do some real work in trying lots of candidate structures, but if you know it's a metallic glass, you probably actually know a little bit Cheers, --Matt ___ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
