[Ifeffit] Linear Combination Fitting using ATHENA

[Matthew Marcus]

Even if all he wants is valence ratio, it would be better if he could fit with the real species.  I could send spectra for magnetite and
maghemite, which will show different Fe valence states, and chromite (natural).
	mam

On 8/12/2013 6:26 AM, Scott Calvin wrote:
> My apologies, Teck Kwang--we seem to be using the term differently. To me, ferrites are a class of compounds, not a particular thing, with magnetite as the paradigmatic form. Magnesium ferrites, like magnetite, adopt the spinel structure.
>
> But I'm realizing I'm not clear on what it is you're trying to determine using LCF. You've said it's the ratio of Fe(II) to Fe(III), but why? What scientific question about your system are you trying to answer? It may be that LCF is not the best technique, and that a fingerprinting technique based on particular features of the spectrum might be more appropriate.
>
> --Scott Calvin
> Sarah Lawrence College
>
> On Aug 12, 2013, at 12:36 AM, Teck Kwang Choo <teck.kwang.choo at monash.edu<mailto:teck.kwang.choo at monash.edu>> wrote:
>
> That's magnetite unfortunately!
>
>
> On 12 August 2013 14:02, Scott Calvin <scalvin at sarahlawrence.edu<mailto:scalvin at sarahlawrence.edu>> wrote:
> Yes it does, Teck Kwang: http://millenia.cars.aps.anl.gov/cgi-bin/newville/Model-Search.cgi/ModelData/fe3o4_rt01_mar02.xmu
>
> --Scott Calvin
> Sarah Lawrence College
>
> On Aug 11, 2013, at 11:12 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:
>
> The database: http://cars.uchicago.edu/~newville/ModelLib/search.html<http://cars.uchicago.edu/%7Enewville/ModelLib/search.html> does not seem to have Ferrite.
>
> The matrix of my sample is largely Mg-ferrite where Fe is in the form of Fe (III). If you anyone has the spectra for Mg-ferrite, would it be possible to provide it to me? Otherwise, I do not think my sample spectra would be useable at all!
>
> Thanks and kind regards.
>
>
> On 10 August 2013 02:21, Matthew Marcus <mamarcus at lbl.gov<mailto:mamarcus at lbl.gov><mailto:mamarcus at lbl.gov<mailto:mamarcus at lbl.gov>>> wrote:
> I would guess that you need better standards.  In particular, FeO is not your typical Fe(II) mineral or oxide.  What is the system you're working on?
> I have an extensive collection of Fe XANES reference spectra, including a number of Fe(II) species.
>
> LCF gives you the fraction of Fe atoms included in the sample.  For example, suppose you had a sample which was genuinely a mix representable
> as FeO.Fe2O3.  Then, LCF would properly report 2/3 Fe2O3 + 1/3 FeO because 2/3 of the Fe atoms are in the Fe2O3 fraction.
>          mam
>
>
> On 8/8/2013 8:37 PM, Teck Kwang Choo 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!
>
>
>
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