[Ifeffit] Alloy EXAFS data fitting

[Frenkel, Anatoly]

resending, now typing more carefully:

***
Hey Xianqin,

If it is a (bulk) alloy system, and if A-A and A-B are 1NN pairs, then, unless there is a phase transition or other perturbations that can involve chemical changes either within the sample of heterogeneous (say, nanophase formation of different composition) or homogeneous (say, ordering changes from random solid solution to an intermetallic compound, as in Au3Cu etc.) nature, the coord. numbers should stay the same. Thus, it is not physical to vary them independently. Thus, if the coord. number of the A-1NN is 12 (as in fcc) then set NB=12-NA and worry only if NA comes out to be outside the range between 0 and 12.

Anatoly

-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov]On Behalf Of XQ WANG
Sent: Thursday, August 31, 2006 2:54 PM
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] Alloy EXAFS data fitting


Dear all,

I am trying to understand some EXAFS data collected on an alloy system 
(sorry I can't say it since these are not my data).

It is a two-element alloy system, name AB.  Their fitting results showed 
that A-B coordination number and A-A coordination number did not follow the 
similar trend with the temperature increase. I am just wondering if this 
case is possible?   I had thought if A-A and A-B are from the same compound, 
they should follow the same trend. Maybe I am wrong.

Another question is whether it is OK to combine coordination of A-A in A 
compound with CN of A-A in AB alloy if these two A-A bond distances are very 
close? If this case is OK, then combination of A-A CN and CN of A-B could 
follow differnt trend (I guess). But I thought we could not combine CN from 
different materials. Maybe I am wrong again??

Please let me know any suggestions concerning this situation.

Thanks!

Xianqin

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