[Ifeffit] Alloy EXAFS data fitting

[XQ WANG]

Thanks, Anatoly, Matt.

This is metallic alloy system.

I am thinking, if there is no phase changes and both CN of A-A and A-B 
increase with temperature increase, that would indicate the increase in 
nanosizes, as Anatoly hinted.

If in AB alloy, A/B ratio is variable, but still in the same structure 
system, CN (A-A)+CN(A-B)=constant should be valid. This indicates the 
exisitence of atom replacement.

If  A/B ratio is variable, and the alloy structure also changes (phase 
transition happens), can we get something like: CN of A-B uniformly 
decreases, while CN of A-A decreases first and then increases as a function 
of temperature? (I guess this might be possible)

When I read the figures, it was not specified that CNs were from different 
phases.  I was confused.

Thanks again, Anatoly, Matt. If my understanding was not quite right, please 
correct me.

Have a great day,

Xianqin





>From: "Matt Newville" <newville at cars.uchicago.edu>
>Reply-To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
>To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
>Subject: Re: [Ifeffit] Alloy EXAFS data fitting
>Date: Thu, 31 Aug 2006 14:55:50 -0500
>
>Dear Xianqin,
>
>Anatoly answered much of this, but I'll add a little more:
>
>>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.
>
>It's hard to say much without more system details (glass, crystal?),  but
>it seems strange to see a temperature dependence of a coordination
>number.  Most crystals would not have any change in CN with
>temperature except at structural phase transitions.   As Anatoly said,
>there may be an exchange of one atom for  another, but the total CN =
>CN(A-A) + CN(A-B) would be constant.
>
>>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??
>
>I would say it's not OK to do this.  The Ag-Ag coordination number from
>pure Ag (ie, 12), would not apply for Ag-Ag coordination in Au0.9Ag0.1,
>though the Ag-Ag bond distance would apply.
>
>--Matt
>_______________________________________________
>Ifeffit mailing list
>Ifeffit at millenia.cars.aps.anl.gov
>http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

_________________________________________________________________
All-in-one security and maintenance for your PC.  Get a free 90-day trial!   
http://www.windowsonecare.com/trial.aspx?sc_cid=msn_hotmail