[Ifeffit] Linear Combination Fitting using ATHENA

Teck Kwang Choo teck.kwang.choo at monash.edu
Thu Aug 15 07:07:51 CDT 2013


Hello again. Just want your opinion on a thought that I have. Due to the
absence of Mg-ferrite (MgFe2O4) K-edge XANES spectrum, I have decided to do
my Fe(II)/Fe(III) quantification with only maghemite and magnetite as
end-member standards.

Because Fe in MgFe2O4 exists entirely as Fe(III) and its structure is the
same as both magnetite and maghemite (inverse-spinel structure with Fe
(III) occupying both tetrahedral and octahedral sites), I am inferring that
its K-edge XANES spectrum would be similar to that of maghemite.

I am planning to take the quantified fraction of maghemite as a sum of the
contributions of maghemite and Mg-ferrite.

For instance, from Linear Combination Fitting:

Fraction of Magnetite=0.05, Fraction of Maghemite = 0.95;
Due to absence of Mg-ferrite spectrum, i will be taking (Fraction of
Maghemite) + (Fraction of Mg-ferrite)= 0.95

What are your thoughts on this?

Kind regards.

Teck Kwang


On 14 August 2013 18:46, Matthew Marcus <mamarcus at lbl.gov> wrote:

> **
> Yup.  That's consistent.  That sort of thing is why every XANES paper
> should state clearly
> the basis of the energy calibration.  With Newville's database, you can
> often figure that
> out yourself because many of the spectra were done with a reference foil.
>     mam
> ----- Original Message -----
>
> *From:* Teck Kwang Choo <teck.kwang.choo at monash.edu>
> *To:* XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> *Sent:* Wednesday, August 14, 2013 1:07 AM
> *Subject:* Re: [Ifeffit] Linear Combination Fitting using ATHENA
>
> Yes Matthew, I used 7112 eV for my Fe K-edge calibration. I am guessing
> that is the reason a ~+1 eV shift in your maghemite spectrum is required is
> required to fit mine. Both pre-edge features match in the sense that they
> are roughly bound by the same energy values.
>
>
> On 14 August 2013 17:30, Matthew Marcus <mamarcus at lbl.gov> wrote:
>
>> **
>> That depends on the way you did your calibration.  If it really matches,
>> including the
>> pre-edge features, with a 1eV shift, then that's what you probably have.
>> Did you take
>> into account my calibration, which puts the Fe K-edge at 7110.75eV?  Some
>> people use other
>> values like 7112eV.
>>     mam
>>
>>  ----- Original Message -----
>> *From:* Teck Kwang Choo <teck.kwang.choo at monash.edu>
>> *To:* XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
>>  *Sent:* Tuesday, August 13, 2013 9:20 PM
>> *Subject:* Re: [Ifeffit] Linear Combination Fitting using ATHENA
>>
>>   Also Matthew, I have found that my sample spectrum is an almost exact
>> replica of the maghemite spectrum, the only differences being the
>> absorbance height of the edge-peak (highest peak), which is ok but more
>> importantly
>> I have found that there is a +1eV shift of my spectrum relative to the
>> maghemite one, probably due to slight differences in beamline. Do you think
>> it is alright to make a +1 eV shift to the maghemite spectrum (or -1eV
>> shift to my sample spectrum)?
>>
>> Thanks.
>>
>> Kind regards.
>>
>> Teck Kwang
>>
>>
>> On 14 August 2013 10:07, Teck Kwang Choo <teck.kwang.choo at monash.edu>wrote:
>>
>>>  Thanks Matthew for the spectra.
>>>
>>> Is it correct to use the spectra that was taken in transmission mode
>>> (the one you did) to fit those taken in fluorescence mode (my case)?
>>>
>>> Teck Kwang
>>>
>>>
>>> On 14 August 2013 01:37, Matthew Marcus <mamarcus at lbl.gov> wrote:
>>>
>>>> Here are reference spectra.  The calibration is defined with the Fe
>>>> metal edge at 7110.75eV.  The maghemite spectrum has been corrected for mild
>>>> overabsorption by reference to magnetite, which is very similar.  The
>>>> magnetite is synthetic Fe3O4 from Aldrich, and done in TEY, so no
>>>> overabsorption.
>>>> The maghemite is from oxidation of Fe oxide nanoparticles and has been
>>>> verified by XRD and comparison with the ETH group's maghemite spectrum.
>>>>         mam
>>>>
>>>>
>>>> On 8/13/2013 1:33 AM, Teck Kwang Choo wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> @Drew Latta: I was wondering why the end members should be magnetite
>>>>> and maghemite. Is it because they are both of inverse-spinel structure, the
>>>>> difference only being that the latter has all Fe completely oxidized into
>>>>> Fe(III)? Would you be able to provide the standard spectra to me if that is
>>>>> the case? Thanks very much!
>>>>>
>>>>> Previously I have only thought of using hematite (alpha-Fe2O3) and FeO
>>>>> as end-members, both representing Fe(III) and Fe(II) respectively without
>>>>> giving much thought to the structure Fe takes. I also had my doubts using
>>>>> magnetite (Fe3O4) as a standard as it is a mixture of both Fe (II) and Fe
>>>>> (III). But thanks to the insights Drew has given, I now think I should take
>>>>> the Fe-coordination environment into account with the use of magnetite and
>>>>> maghemite as standards.
>>>>>
>>>>> @Alexandre and Matthew: I have obtained Mossbauer spectra of some of
>>>>> my samples but like Drew said, it is not straightforward at this point in
>>>>> time. Will see what I can do with the data I have!
>>>>>
>>>>> Thanks for all your responses! It is greatly appreciated! This forum
>>>>> has been more helpful than I thought!
>>>>>
>>>>> Teck Kwang
>>>>>
>>>>>
>>>>> On 13 August 2013 01:34, Matthew Marcus <mamarcus at lbl.gov <mailto:
>>>>> mamarcus at lbl.gov>> wrote:
>>>>>
>>>>>     While it's true that Mossbauer is the gold standard for Fe valence
>>>>> determination, access to the technique isn't all that common, and I don't
>>>>> know
>>>>>     of any facility that can do it on a micro scale.  Is there one?
>>>>>              mam
>>>>>
>>>>>
>>>>>     On 8/12/2013 7:01 AM, Alexandre dos Santos Anastacio wrote:
>>>>>
>>>>>         Hello,
>>>>>
>>>>>         maybe that fingerprinting technique would be Mossbauer
>>>>> spectroscopy. The Fe(II)/Fe(III) ratio comes easily and also there are lots
>>>>> of papers about Mg-ferrite, an example:
>>>>>
>>>>>         10.1109/TMAG.2009.2018880 <http://dx.doi.org/10.1109/__**
>>>>> TMAG.2009.2018880 <http://dx.doi.org/10.1109/__TMAG.2009.2018880> <
>>>>> http://dx.doi.org/10.1109/**TMAG.2009.2018880<http://dx.doi.org/10.1109/TMAG.2009.2018880>
>>>>> >>
>>>>>
>>>>>         Alexandre.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teck Kwang Choo
>>>>> PhD Student
>>>>> Department of Chemical Engineering
>>>>> Room 225, Building 36
>>>>> Monash University
>>>>> Mobile No.: 04-11489904
>>>>>
>>>>>
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>>>
>>>
>>> --
>>> Teck Kwang Choo
>>> PhD Student
>>> Department of Chemical Engineering
>>> Room 225, Building 36
>>> Monash University
>>> Mobile No.: 04-11489904
>>>
>>
>>
>>
>> --
>> Teck Kwang Choo
>> PhD Student
>> Department of Chemical Engineering
>> Room 225, Building 36
>> Monash University
>> Mobile No.: 04-11489904
>>
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>
>
> --
> Teck Kwang Choo
> PhD Student
> Department of Chemical Engineering
> Room 225, Building 36
> Monash University
> Mobile No.: 04-11489904
>
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-- 
Teck Kwang Choo
PhD Student
Department of Chemical Engineering
Room 225, Building 36
Monash University
Mobile No.: 04-11489904
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