Dear everyone
I would like to use EXAFS data to analyze how the positive electrode active material undergoes local structural changes during the redox reaction of the positive electrode active material. I have three questions.
1. Structural data such as CIF files and EXAFS data often do not match. When determining R as a fitting parameter, which should be trusted for fitting, structural data or EXAFS?
2. What do you think about changing the fitting parameters?
3. What is the accuracy of fitting and what is the minimum accuracy required?
Hi Takeshi Shimizu
The EXAFS fittings can turn tricky and need some prior knowledge about structure and behavior of system.
1. I would suggest you to first think about all possible changes in structure to finally decide for structure model. EXAFS gives you short range information about the local structure of the core atom. So, if you have all possible model for the expected or suspected changes in structure of material, you can initiate EXAFS fitting with that.
2. Regarding fitting parameters, you must be aware of interplay of various paths. Eg. If you are having more than one paths in first shell but those are supposed to be behaving in similar way, then you can have common parameters (radial distance correction, Debye Waller factor) for those. And same is the case for next coordination shell. And the values of these parameters must be in tolerable range. Sometimes we end up with excellent fitting with illogical parameters. So, parameters must be in legitimate range.
3. When you feel like parameters are in defendable range and both experimental and theoretical curves are showing good agreement, you can freeze the fitting at that point. This step is discretionary and may vary for you and me.
Best wishes.
Dear Manju Bhatia,
Thank you for your detail answers.
EXAFS fitting is difficult for me, but I'm satisfied to know how to analyze EXAFS data.
Dear Artur Braun,
Thank you for your instructive suggestion. I'm not the expert for XAFS. I'm relieved not to try EXAFS fitting by myself because it would take much time to fit the unsolved EXAFS data.
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