I'm starting to analyze some XAFS experimental data measured from an amorphous sample. The target element was Ba and the measurement was performed over the LIII edge. Can someone orient me on how to proceed with amorphous material XAFS analysis? I've tried some ideas with no success... I have the crystalline .CIF file of the compound, but in my samples I have both crystalline and amorphous phases.
Any ideas and bibliography will be appreciated.
Thanks in advance
XAFS (EXAFS &XANES) cannot differentiate between crystalline or amorphous material because it is a short range order analysis technique up to a very few coordination spheres. Gathering detailed informations from the third or even fourth coordination sphere here is a very challenging task.
You get the oxidation state (of the target element) via XANES and very few distances (with respect to the target element) and coordination numbers via EXAFS.
For the case of a partly crystalline/amorphous sample you will get some kind of mean values for the mentioned parameters averaged over all phases.
For an introduction (including data evaluation) please have a look at:
Article XAFS Spectroscopy: Fundamental Principles and Data Analysis
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=2ahUKEwjXu9nr-NTiAhUI6qQKHUlyATwQFjACegQIAhAC&url=http%3A%2F%2Fwww.esrf.eu%2Ffiles%2Flive%2Fsites%2Fwww%2Ffiles%2Fevents%2Fconferences%2F2017%2FUser_Meeting_2017%2FPart%2520I%2520.pdf&usg=AOvVaw3n9AUSMhjmdN9rAfFPEwbZ
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwjXu9nr-NTiAhUI6qQKHUlyATwQFjABegQIBBAC&url=http%3A%2F%2Fwww.esrf.eu%2Ffiles%2Flive%2Fsites%2Fwww%2Ffiles%2Fevents%2Fconferences%2F2017%2FUser_Meeting_2017%2FPart%2520II%2520.pdf&usg=AOvVaw3q-ioxaazlIfTKaP2ZVIuK
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwiSroyb0d7iAhXw0eAKHaZsAs4QFjAAegQIARAC&url=http%3A%2F%2Fwww.esrf.eu%2Ffiles%2Flive%2Fsites%2Fwww%2Ffiles%2Fevents%2Fconferences%2F2017%2FUser_Meeting_2017%2FPart%2520III.pdf&usg=AOvVaw1JP07Cee-q3MmA2Cd0wdgt
https://www.researchgate.net/deref/https%3A%2F%2Fwww.bnl.gov%2Fps%2Fworkshops%2FXAFS2014%2F87.pdf
I know that this is a quite vague answer and you certainly know already a lot about XAFS data evaluation.
You might be a bit more specific in your question.
you can do it by athena program, and ft of xafs gives you local structure around the target element. so the ft of xafs didnt give an expected graphs as crystalline materials. so as my knowledge, you only gives an information about valence state of ba ions and it may obtain a short range bond structure around ba ions and it will change when you changed the surface region of the sample
When you will fit your data, you may need slightly more complex models than the usual ones. If I remember correctly, for an amorphous material, the bond length distribution is much broader than for a crystalline one, hence the approximation leading to the Debye-Waller factor term in the EXAFS part may not hold. So you may have to add so-called "cumulants" additionnal terms.
Gerhard Martens , thank you for your reply. I've been to one of Pascarelli's courses long time ago, I will definitely check out those slides in detail. I know the question was quite vague, so I wasn't expecting a better answer than the one you gave me. I was a bit concerned, because of Bruce Ravel's video tutorials, in which he gives an example of the data analysis treatment given to an amorphous Ge sample (https://www.youtube.com/watch?v=GPDFzSrNeE8&t=1415s). I was wondering how it would change by having both amorphous and crystalline phases in the sample, and what the parameters would represent in this case. I was also wondering if there was a standardized procedure as to analyze this type of data, but by your answer I get the impression that there isn't.
Nonetheless, Emmanuel Curis has captured by attention with the cumulants additional terms. Could you please reference any article/book in which a discussion about these terms is given?
Thank you all for your answers.
Jose Robledo : Using « EXAFS cumulants » in google gives a huge amount of candidate papers, recent or quite old. As I'm not a specialist, I will not advise any of them specially, except this old one that presents the underlying theory:
Chapter The EXAFS of Disordered Systems and the Cumulant Expansion
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Powders