On 08/09/2013 08:40 AM, Teck Kwang Choo wrote:

I agree with you that I might have not chosen the right standards for my sample. In fact, XRD analysis have confirmed that Ferrite is the main form of Fe in my sample but I did not have any ferrite standards during XANES analysis. Was wondering if you happen to have any Ferrite XANES spectra by any chance?

Did you look here? http://cars.uchicago.edu/~newville/ModelLib/search.html B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel

Yes it does, Teck Kwang: http://millenia.cars.aps.anl.gov/cgi-bin/newville/Model-Search.cgi/ModelData... --Scott Calvin Sarah Lawrence College On Aug 11, 2013, at 11:12 PM, Teck Kwang Choo mailto:teck.kwang.choo@monash.edu> wrote: The database: http://cars.uchicago.edu/~newville/ModelLib/search.htmlhttp://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 mailto:mamarcus@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! -- 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.govmailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.govmailto: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.govmailto:Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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 mailto:teck.kwang.choo@monash.edu> wrote: That's magnetite unfortunately! On 12 August 2013 14:02, Scott Calvin mailto:scalvin@sarahlawrence.edu> wrote: Yes it does, Teck Kwang: http://millenia.cars.aps.anl.gov/cgi-bin/newville/Model-Search.cgi/ModelData... --Scott Calvin Sarah Lawrence College On Aug 11, 2013, at 11:12 PM, Teck Kwang Choo mailto:teck.kwang.choo@monash.edumailto:teck.kwang.choo@monash.edu>> wrote: The database: http://cars.uchicago.edu/~newville/ModelLib/search.htmlhttp://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 mailto:mamarcus@lbl.govmailto:mamarcus@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!

I would say that the Mossbauer isn't always quite straight forward, especially if the OP is working with nanoparticles. You have to find the right temperature where superparamagnetism is gone but the Verwey transition hasn't occurred to reliably fit the resulting Mossbauer spectra. (I'll assume from ignorance that that Mg-ferrites have Verwey transitions.) I would think the two best end-members for the XAS LC fits are possibly magnetite (fully stoichiometric: Fe2+/Fe3+ = 0.5) and either maghemite (gamma-Fe2O3) or the fully oxidized Mg-ferrite. Which Fe2O3 are you using Teck Kwang Choo? If you are using the alpha-form (hematite) then I would suspect you might not get very good fits as the structural difference between maghemite and hematite significantly influence their XANES spectra. I've had good success finding Fe2+/Fe3+ ratios in partially oxidized magnetites by using magnetite and maghemite as end-members in LC fits. So I think you should have reasonable success for the Mg-ferrites using the right end-members. Contact me in person below, if you are interested in magnetite/maghemite standard spectra. Best, Drew Latta ----------------------------------- Drew E. Latta, Ph.D. Postdoctoral Associate Molecular Environmental Science Group Biosciences Division Argonne National Laboratory Building 203, Room E-105 9700 South Cass Avenue Argonne, IL 60439 Phone: 1-630-252-3985 dlatta@anl.govmailto:dlatta@anl.gov http://www.mesg.anl.gov ----------------------------------- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Alexandre dos Santos Anastacio Sent: Monday, August 12, 2013 9:01 AM To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Linear Combination Fitting using ATHENA 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.2009.2018880http://dx.doi.org/10.1109/TMAG.2009.2018880 Alexandre.

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 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.2009.2018880http://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

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 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 > 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.2009.2018880http://dx.doi.org/10.1109/TMAG.2009.2018880

...

...

Alexandre.

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...

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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

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 To: XAFS Analysis using Ifeffit 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 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 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 mailto:mamarcus@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> Alexandre. _________________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.__gov mailto: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 mailto:Ifeffit@millenia.cars.aps.anl.gov 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 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 -- 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

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 To: XAFS Analysis using Ifeffit 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 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 To: XAFS Analysis using Ifeffit 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 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 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 mailto:mamarcus@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> Alexandre. _________________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.__gov mailto: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 mailto:Ifeffit@millenia.cars.aps.anl.gov 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 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 -- 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

One spectrum was taken in fluorescence mode (maghemite), the other in electron-yield mode. Yes, it's OK to do that on pre-edge subtracted, normalized spectra, which is what I sent. mam ----- Original Message ----- From: Teck Kwang Choo To: XAFS Analysis using Ifeffit Sent: Tuesday, August 13, 2013 5:07 PM Subject: Re: [Ifeffit] Linear Combination Fitting using ATHENA 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 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 mailto:mamarcus@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> Alexandre. _________________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.__gov mailto: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 mailto:Ifeffit@millenia.cars.aps.anl.gov 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 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

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 mailto:teck.kwang.choo@monash.edu> wrote:

That's magnetite unfortunately!

On 12 August 2013 14:02, Scott Calvin mailto:scalvin@sarahlawrence.edu> wrote: Yes it does, Teck Kwang: http://millenia.cars.aps.anl.gov/cgi-bin/newville/Model-Search.cgi/ModelData...

--Scott Calvin Sarah Lawrence College

On Aug 11, 2013, at 11:12 PM, Teck Kwang Choo mailto:teck.kwang.choo@monash.edumailto:teck.kwang.choo@monash.edu>> wrote:

The database: http://cars.uchicago.edu/~newville/ModelLib/search.htmlhttp://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 mailto:mamarcus@lbl.govmailto:mamarcus@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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Unfortunately, ferrite is something I don't have. nan On 8/11/2013 8:12 PM, Teck Kwang Choo 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 mailto:mamarcus@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!

-- 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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