[Ifeffit] Lost second shell

Frenkel, Anatoly frenkel at bnl.gov
Sun Feb 1 21:15:46 CST 2009


 
Eugenio,
 
The possibilities depend on the actual data at hand. Not seeing second shell is a relative term. Do you mean that you do not see it above noise? Then, technically, you cannot say that you do not have a second shell. Er may substitute for Zn and you will still have Er-Zn contributions expected for ZnO structure, but they will be disordered due to the large DWF and thus "hide" under the noise level which can be estimated as the FT magnitude at high r. However, If the data is of high quality, and you see well defined first peak (Er-O) in r-space and have negligible noise level, then you may say, with confidence, that Er does not enter ZnO lattice substitutionally. 
Then, indeed, it may be a surface sorption of some sort which is usually accompanied by high disorder in the second shell, as was shown to be the case in similar examples, e.g., Pb sorption of iron oxides.
 
If you sent an image of your data in k-space and r-space it would be easier to judge.
 
Anatoly
 
 

________________________________

From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of Eugenio Otal
Sent: Sun 2/1/2009 9:52 PM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] Lost second shell


Hi all,
I am working with Er doped ZnO and the EXAFS measurements (Er L3) shows that I have not a second shell when I perform the FT. I checked that the phase is not destroying the signal, and that is not the guilty guy. 
I have two possibilities, that the erbium is segregated on the surface of the particles with a strong disordered phase that destroy second shell information (XANES simulation are different from oxide and hydroxides) or that the atoms are isolated in the surface of the particles.
Should I use the card for molecules for isolated atoms? And for the disordered phase, what can I do?
Is there another possibility to lose the second shell?
Thanks in advance, euG

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