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 <mamar...@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.c...@monash.edu> > *To:* XAFS Analysis using Ifeffit <ifeffit@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 <mamar...@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.c...@monash.edu> >> *To:* XAFS Analysis using Ifeffit <ifeffit@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.c...@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 <mamar...@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 <mamar...@lbl.gov <mailto: >>>>> mamar...@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. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> ______________________________**___________________ >>>>> Ifeffit mailing list >>>>> ifef...@millenia.cars.aps.anl.**__gov <mailto: >>>>> ifef...@millenia.cars.**aps.anl.gov<Ifeffit@millenia.cars.aps.anl.gov> >>>>> > >>>>> http://millenia.cars.aps.anl._**_gov/mailman/listinfo/ifeffit >>>>> <http://millenia.cars.aps.anl.**gov/mailman/listinfo/ifeffit<http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit> >>>>> > >>>>> >>>>> ______________________________**___________________ >>>>> Ifeffit mailing list >>>>> ifef...@millenia.cars.aps.anl.**__gov <mailto: >>>>> ifef...@millenia.cars.**aps.anl.gov<Ifeffit@millenia.cars.aps.anl.gov> >>>>> > >>>>> http://millenia.cars.aps.anl._**_gov/mailman/listinfo/ifeffit < >>>>> http://millenia.cars.aps.anl.**gov/mailman/listinfo/ifeffit<http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> Teck Kwang Choo >>>>> PhD Student >>>>> Department of Chemical Engineering >>>>> Room 225, Building 36 >>>>> Monash University >>>>> Mobile No.: 04-11489904 >>>>> >>>>> >>>>> ______________________________**_________________ >>>>> Ifeffit mailing list >>>>> ifef...@millenia.cars.aps.anl.**gov<Ifeffit@millenia.cars.aps.anl.gov> >>>>> http://millenia.cars.aps.anl.**gov/mailman/listinfo/ifeffit<http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit> >>>>> >>>>> >>>> _______________________________________________ >>>> Ifeffit mailing list >>>> Ifeffit@millenia.cars.aps.anl.gov >>>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >>>> >>>> >>> >>> >>> -- >>> 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 >> >> ------------------------------ >> >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit@millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> >> >> _______________________________________________ >> Ifeffit mailing list >> Ifeffit@millenia.cars.aps.anl.gov >> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit >> >> > > > -- > Teck Kwang Choo > PhD Student > Department of Chemical Engineering > Room 225, Building 36 > Monash University > Mobile No.: 04-11489904 > > ------------------------------ > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > > -- Teck Kwang Choo PhD Student Department of Chemical Engineering Room 225, Building 36 Monash University Mobile No.: 04-11489904
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