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@cmt.anl.gov

...

-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@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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================================== Feng Wang fwang@phys.ualberta.ca Electron Microscopy Group Department of Physics University of Alberta =========================================================