[Ifeffit] Linear Combination Fitting using ATHENA

[Matthew Marcus]

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 <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>>

              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



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