Chris,

That double peak around 8 is normal for Fe (oxyhydr)oxides; see the attached for an example.  Also see Toner et al. 2009 (GCA 73 p 388, Fig 6) for a nice discussion of what structures can make it show up.  I think perhaps you are seeing an oxidation state shift too.

Best of luck with the happiness!

-Leslie

-----Original Message-----
From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Christopher Patridge
Sent: Tuesday, January 15, 2013 6:22 AM
To: XAFS Analysis using Ifeffit
Subject: [Ifeffit] k-range question & R-factor

Hello Users,

I was looking for an opinion about the chi(k) signal in a set of data I am analyzing.  Brief background, this is a set of in-situ XAS data collected at the Fe K edge from a working electrochemical cell at a range of potentials during charge; I did not collect the data. I suspect the feature at ~ 8 angstroms-1, although present in all the spectra is noise or glitch and wondered if I am being overly cautious?

My conservative range ( k = 2-7 and R = 1-2) really constrains the model Nidp = 3.31.  Luckily, multiple datasets ( 8 ) to the rescue to give me some flexibility.  In a multiple dataset fitting, is the R-factor of the whole set just the average or total mismatch across all the datasets or it calculated another way?

Working towards happiness,

Chris Patridge

--

********************************

Christopher J. Patridge, PhD

NRC Post Doctoral Research Associate

Naval Research Laboratory

Washington, DC 20375

Cell: 315-529-0501

**

Leslie L. Baker, Ph.D.

Department of Plant, Soil and Entomological Sciences

and Department of Geological Sciences

University of Idaho

875 Perimeter Drive MS 2339

Moscow, ID 83844-2339

208-885-9239

http://scholar.google.com/citations?user=ejpH5p0AAAAJ