Re: [Ifeffit] [Ext] Re: Question about mixed second coordination shell

Hi Eugenio: This looks like a layered structure, most likely a P2 or P3 phase. Is this correct? How sure are you that you have a single phase and that the Na ions are well ordered? Is it possible that there is so much disorder in the M-Na distances that they wash out any contribution? In that case, the second M-O distance would probably be more important. You also do not mention if this is Ni, Fe or Mn edge data. Is it possible that these differ? Carlo On Tue, Jan 16, 2024 at 11:30 PM Otal Eugenio wrote:

Dear Robert, Thanks for your detailed answer. I am cutting at R=3.35. I also tried to go up to 4.0 to provide more freedom and to include the SS TM-O at 3.6. It seems that including MS was not fruitful at the moment. I found the contribution very tiny, Importance < 10. I included the path at 3.6, and it fits well, but when I include the Na, the CN_Na goes to high values (>10) and errors (~+/- 50) I also tried to restrict the CN of TM to force the Na to take place and get good results. Also useless. I was checking the data in R_real and the TM and Na paths. I see the TM path is in phase while the Na path is not. I wonder if this is affecting the fit. How should I constrain the fitting to solve this situation? Best regards.

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On Wed, Jan 17, 2024 at 1:24 AM Robert Gordon wrote:

...

Hi Otal,

I ran a quick FEFF simulation just to see what is present under that second peak in the FT. There are many more shells than just TM and Na...e.g.

There is significant multiple scattering and another backscattering peak (Fe-O) at 3.6Angstroms. All of these are going to spread underneath that peak in the FT. You might also be getting some interference from the 4.07A MS stuff. It doesn't seem a surprise that just including TM and Na is giving problems.

What is your high-R cutoff? Have you tried including multiple-scattering or that 4th backscattering contribution?

cheers, Robert

On 2024-01-09 12:06 a.m., Otal Eugenio wrote:

Dear all, Happy New Year! I am dealing with the fitting of NaMn0.3Fe0.4Ni0.3O2 second shell. I have Mn, Ni, and Fe at 2.9772Å and Na at 3.1859Å, showing only one shell. If I use any of the transition metals (dZ <5) for fitting the second coordination shell. fitting is fine, but when I introduce the Na path, the fitting has no sense, CN_Na grows and also its error. Even including Na, I have Nvary = 10 and Ninp = 13.98, so I am getting out of ideas and nothing helpful in the ifeffit Archive until now. Is there any strategy for dealing with mixed second coordination shells? I am attaching the file exported from Larch and the cif file. Best regards.

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Eugenio H. OTAL Assistant Professor Dept. of Materials Chemistry Shinshu University 4-17-1 Wakasato, Nagano 380-8553, JAPAN eugenio_otal@shinshu-u.ac.jp https://sites.google.com/view/zettsu-laboratory/news-updates

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