[Ifeffit] Lost second shell

[Carlo Segre]

Hi Eugenio:

In this case, you probably have to take advantage of other information you 
might have about your samples.  You say that the lattice parameter of the 
ZnO does not change.  Depending on the nominal doping percentage of the 
Er, this could be a good indication that the Er is not incorporated.  You 
also don't state whether the ZnO is in nanoparticle form or bulk.  This 
will make a significant difference on whether you expect to see real 
substitution.

We have taken data on Er doped films of ZnS.  In that case, the first 
shell was much sharper than yours and the Er-Zn distances much more 
prominent even though we discovered that the Er significantly distorts the 
ZnS structure.  We also have measured Mn doped ZnO nanoparticles where the 
Mn was not incorporated into the ZnO structure at all but on the surface 
while the same Mn atom doped into a bulk sample was incorporated into the 
ZnO structure.

The first thing I would try is to see, as Anatoly suggests, what the Er-O 
coordination number and bond distance comes out to be when you fit the 
first shell.  You can compare this with Er2O3.

Cheers,

Carlo

On Mon, 2 Feb 2009, Frenkel, Anatoly wrote:

> Eugenio,
>
> Nice plots, and good data too, with a low amount of noize. It is indeed 
> a very sad looking Er-O contribution and almost nothing else except for 
> a small bump near 3 A where Zn-Zn appears in ZnO. For Er-O, the peak 
> position is shifted to the right relative to a nominal Zn-O position in 
> ZnO (at around 1.5 A, not correcting for the phase shift), as expected 
> due to the larger size of Er ions compared to Zn.
>
> Thus, because of that bump at 3 A it is not really a clear cut situation 
> where you can tell confidently that Er does not substitute for Zn. 
> However, in ZnO, the Zn-Zn peak is higher in intensity than Zn-O, while 
> here it is much much lower. Thus, if Er does substitute for Zn, the 
> entire Er-O cage must be displaced from a high symmetry position 
> relative to Zn atoms in order to produce large disorder in Er-Zn pair 
> lengths that causes reduction of Er-Zn single scattering contribution to 
> EXAFS and, in turn, explains the small bump at 3A. It would also help 
> you if you found the coordination number of Er-O pairs and compared it 
> with that of Zn-O in ZnO.
>
> Anatoly
>
>
>
> ________________________________
>
> From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of Eugenio Otal
> Sent: Mon 2/2/2009 8:34 PM
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] Lost second shell
>
>
> Anatoly,
> Here I attach some pictures.
> I also have luminescence measurements an found a great disorder but I could not find changes in the cell parameters by XRD refinements. I perfored XANES simulations for ZnO sustituted by Er and the spectra is really different. I cannot believe that the Er is in Zn site, but maybe the structure changes and the simulation is not so "real".
>
> euG
>
>
>
>
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-- 
Carlo U. Segre -- Professor of Physics
Associate Dean for Special Projects, Graduate College
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://www.iit.edu/~segre   segre at debian.org