[Ifeffit] Odd feff result

[Feng Wang]

Hi Scott and Jeremy

It is interesting result, and I strongly agree with Jeremy's explanation. We 
also notices such a phonomenon before, a prominent postpeak, about 40 eV 
above iron L3 edge, even in very thin films of iron fluoride. The peak 
gradually disappears as fluorine is removed by electron irradiation, but 
appears when an iron film is oxidized.Oxygen and fluorine anions in 
transition-metal compounds are strong backscatters, as confirmed by the FEFF 
calculation, I believe boron is another strong scatter. 

Best regards,

Feng 

> Scott,
> 
> This doesn't seem like too unusual a result to me.  The amp ratio from
> feff is more of a qualitative than a quantitative prediction.  Now I am
> just making a guess; nevertheless, a boron scattering path will probably
> have a significantly higher amplitude at low k compared to a Ni or Fe
> scattering path.  This could easily be the cause of the difference you
> observe.
> 
> Jeremy Kropf
> 
> Chemical Engineering Division
> Argonne National Laboratory
> Argonne, IL 60439
> 
> Ph: 630.252.9398
> Fx: 630.252.9373
> kropf at cmt.anl.gov
>  
> 
> > -----Original Message-----
> > From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> > [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> > Of Scott Calvin
> > Sent: Friday, March 24, 2006 1:01 PM
> > To: XAFS Analysis using Ifeffit
> > Subject: [Ifeffit] Odd feff result
> > 
> > Hi all,
> > 
> > I just ran a feff calculation using feff6L and got a result 
> > that surprised me a little. I was modelling a ferrite with a 
> > nickel and boron substituted for iron in a small fraction of 
> > sites. Here's part of files.dat:
> > 
> >      file        sig2   amp ratio    deg    nlegs  r effective
> >   feff0010.dat 0.00000     2.706     2.000     3   3.7141
> >   feff0011.dat 0.00000    26.472    20.000     3   3.7141
> >   feff0012.dat 0.00000     4.038     2.000     3   3.7141
> > 
> > and the corresponding part of the paths.dat:
> > 
> >      10    3   2.000  index, nleg, degeneracy, r=  3.7141
> >        x           y           z     ipot  label      rleg    
> >   beta        eta
> >     -3.126710    1.042240    1.042240   1 
> > 'Ni    '     3.4567  150.5039    0.0000
> >     -1.146460    1.146460    1.146460   3 
> > 'O     '     1.9857   58.9923    0.0000
> >      0.000000    0.000000    0.000000   0 
> > 'Fe    '     1.9857  150.5039    0.0000
> >      11    3  20.000  index, nleg, degeneracy, r=  3.7141
> >        x           y           z     ipot  label      rleg    
> >   beta        eta
> >      1.042240   -3.126710    1.042240   2 
> > 'Fe    '     3.4567  150.5039    0.0000
> >      1.146460   -1.146460    1.146460   3 
> > 'O     '     1.9857   58.9923    0.0000
> >      0.000000    0.000000    0.000000   0 
> > 'Fe    '     1.9857  150.5039    0.0000
> >      12    3   2.000  index, nleg, degeneracy, r=  3.7141
> >        x           y           z     ipot  label      rleg    
> >   beta        eta
> >     -1.042240    3.126710    1.042240   4 
> > 'B     '     3.4567  150.5039    0.0000
> >     -1.146460    1.146460    1.146460   3 
> > 'O     '     1.9857   58.9923    0.0000
> >      0.000000    0.000000    0.000000   0 
> > 'Fe    '     1.9857  150.5039    0.0000
> > 
> > So here's the question. These three paths are identical 
> > except for the identity of one of the scattering atoms. The 
> > degeneracy of the path with boron and the path with nickel is 
> > the same. Why is the feff amplitude ratio for the 
> > boron-containing path higher than that of the 
> > nickel-containing path? Shouldn't nickel scatter more 
> > strongly? And yes, I double-checked...the potentials are 
> > defined correctly in the feff.inp file.
> > 
> > --Scott Calvin
> > Sarah Lawrence College
> > 
> > _______________________________________________
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> > Ifeffit at millenia.cars.aps.anl.gov
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> > 
> 
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==================================
Feng Wang
fwang at phys.ualberta.ca
Electron Microscopy Group
Department of Physics
University of Alberta
=========================================================