[Ifeffit] Exafs spectra Fitting of WO3 nanoparticles

[Abdallah Nassereddine]

Dear all,

Good morning,

I try to Fit EXAFS spectra of a sample composed of supported tungsten 
oxide ( WO3/ZSM-5) nanoparticles obtained by operando studies under gas 
(CH4, He) at 750 °C.

First, and after several trials, I analyzed the WO3 reference spectrum 
obtained at room temperature and I succeeded in determining the 
amplitude (S0) by using the monoclinic structure WO3 cif file.

Then, I used the value of this amplitude obtained to be able to fit the 
structural parameters (coordination number N, Debye-waller Factor, 
Interatomic distance) of WO3/ZSM-5 nanoparticles under gas, but I can't. 
  the best result I got was by selecting the first two shells (at 1.858 
and 1.919 Angstrom) of the monoclinic structure. However, with all the 
optimizations, the Debye-waller factor obtained for the second W-O shell 
(1.919 Angstrom) is always negative, and if I don't take this shell into 
account, I completely lose my Fit.

Have any of you ever worked on this type of sample and might have an 
idea that would help me improve my Fit?

Thank you in advance,

Best regards,

Abdallah Nassereddine
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