[Ifeffit] Linear combination fitting

Scott Calvin SCalvin at slc.edu
Tue Apr 7 09:44:27 CDT 2009

Hi Guven,

This is not unusual, in my experience, particularly if the chi(k) fit  
is not particularly good.

XANES and EXAFS are sensitive to different aspects of the local  
environment. In  particular, the chi(k) is much more affected by  
structure beyond the nearest-neighbors. In your system, it is unlikely  
that you "really" have a mixture of bulk ZnO and bulk ZnTiO3. For  
nearest neighbors, those two standards may be good enough, and may  
give you a decent fit to XANES that has some physical meaning. But for  
chi(k) those standards may not be sufficient, and, while the fit is  
doing what it can, the fractions may not be particularly physically  
meaningful. One piece of evidence that this is going on is if the  
chi(k) fit is "poor," that is, if the fitted chi(k) does not  
correspond well to the data.

--Scott Calvin
Sarah Lawrence College

On Apr 6, 2009, at 5:31 PM, Guvenc Akgul wrote:

> Dear all,
> I have done Ti doped ZnO EXAFS data analysis but I guess it  is  
> getting mixture structure at high concentration for example 55% Ti  
> doped ZnO.Also I done linear combination fit , but at  fitting space  
> norm(E),ZnO weight is 0.779 and ZnTiO3 is 0.221 then I changed  
> fitting space is chi(k)  ZnO weight is getting 25.2 and ZnTiO3 is  
> getting 74.8 and it is not same like at fitting space norm(E) why?

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