[Ifeffit] EXAFS reference materials
frenkel at bnl.gov
Thu Mar 22 14:28:55 CDT 2007
I am cc'ing this email to IFEFFIT mailing list. There are several reasons (I am listing just a few) you should measure a reference sample simultaneously with unknown materials.
1) to align the unknown sample scans prior to merging. If those data are noisy, reference sample can be used for the alignment. In addition, if you want to compare samples before and after some changes that may affect their energy positions (e.g., oxidation, reduction, doping, metal-insulator transition, etc.) you want to align all of their references to reliably analyze these changes.
For this purpose, it does not matter whether you use a metal or a metal oxide or any other standard with the same resonant element.
2) to find S02 value. It is usually the same in most samples which have the same resonant element.
For this purpose, what matters the most is whether you can reliably find S02 from your standard (and then impose it on your unknown sample). Thus, some exotic reference which may still be good for 1) may not be as good for 2) since it may be difficult to refine its structure and get precise value for S02. The metals would be the best, but if you have other materials with "open lattices", e.g., fcc, rock salt, etc., with well defined first shell that you can fit with the miniumum parameters, they will all work fine.
3) to use as a model for your analysis.
If you analyze an alloy, as in your case, you want to compare EXAFS results in your alloys against those in relevant pure compounds. For binary alloys, the best reference will be a pure metal, for ternary - an intermetallic compound, etc. An oxide would not be so useful for modeling. For that reason, people often measure more than one reference, as per 1),2) and 3).
Hope it helps,
From: rh2rr at virginia.edu [mailto:rh2rr at virginia.edu]
Sent: Thu 3/22/2007 2:54 PM
To: Frenkel, Anatoly
Subject: EXAFS reference materials
Dear Dr. Frenkel,
I'll do EXAFS on metallic glass but I am not sure about the reference
We are trying to study structural relaxation of metallic glass by EXAFS. My
samples are Al-TM-RE (TM=Fe,Co,Ni, RE=Gd,Ce,Y). Because Ce and Y are easily
oxidized in air, some people suggest use cerium oxide and yttrium oxide as
reference materials. My question is: when I do EXAFS measurement and data
analysis, is METAL necessary for reference materials, or METAL OXIDE is
fine as reference?
Your kind help would be greatly appreciated.
Materials Science and Engineering
University of Virginia
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