[Ifeffit] Fwd: Linear Combination Fitting using ATHENA

[Scott Calvin]

I just noticed part of this thread went off-list. That's easy to do by mistake sometimes. I'm forwarding this part of the exchange to the list so that we don't start talking too much in circles.

--Scott Calvin
Sarah Lawrence College

Begin forwarded message:

From: Scott Calvin <scalvin at sarahlawrence.edu<mailto:scalvin at sarahlawrence.edu>>
Subject: Re: [Ifeffit] Linear Combination Fitting using ATHENA
Date: August 9, 2013 8:54:59 AM EDT
To: Teck Kwang Choo <teck.kwang.choo at monash.edu<mailto:teck.kwang.choo at monash.edu>>

Hi Teck Kwang,

An Fe3O4 spectrum is available at the CARS XAFS database:  http://cars.uchicago.edu/~newville/ModelLib/search.html

--Scott Calvin
Sarah Lawrence College

On Aug 9, 2013, at 8:35 AM, Teck Kwang Choo <teck.kwang.choo at monash.edu<mailto:teck.kwang.choo at monash.edu>> wrote:

Hi Scott,

My spectrum standard fits extremely well with FeO: the sample spectrum's conformation to FeO's can be seen even by just superimposing both spectra together. Through XRD, it was confirmed that Ferrite (-Fe2O4) is the primary form of Fe but unfortunately I did not have any Ferrite standard compound with me during the actual XANES analysis.

I am now suspecting that both FeO and -Fe2O4's spectra might be similar to each other. Do you have the spectrum for ferrite (Mg-ferrite if possible) by any chance?

Thanks and kind regards.

Teck Kwang


On 9 August 2013 21:00, Scott Calvin <scalvin at sarahlawrence.edu<mailto:scalvin at sarahlawrence.edu>> wrote:
Hi Teck Kwang,

Molar percent by absorbing atom. In other words, if the best fit is 60% Fe(II), that corresponds to 60% of the iron atoms being Fe(II).

But note that XANES depends on more than just valence state. Does the FeO and Fe2O3 combination fit the XANES well? Do those compounds correspond well to the actual compounds expected in the material? Did you try other iron standards?

--Scott Calvin
Sarah Lawrence College


On Aug 8, 2013, at 11:37 PM, Teck Kwang Choo <teck.kwang.choo at monash.edu<mailto:teck.kwang.choo at monash.edu><mailto:teck.kwang.choo at monash.edu<mailto:teck.kwang.choo at monash.edu>>> wrote:

Hello,

I have been using ATHENA to perform Linear Combination Fitting (LCF) on my XANES spectrum to quantify the amounts of Fe (II) and Fe (III) in my samples using only FeO and Fe2O3 as standards. The results showed a majority of Fe (II), which is contrary to what was expected.

This made me wonder if the LCF results from XANES is a molar percentage (mol %) or weight percentage (wt%).

Could anyone enlighten me on this matter?

Thanks!

--