> Date: Thu, 18 Sep 2014 09:04:17 -0400
> From: bravel@bnl.gov
> To: ifeffit@millenia.cars.aps.anl.gov
> Subject: Re: [Ifeffit] Inconsistency of the amplitude reduction factor
>
> On 09/18/2014 07:23 AM, Scott Calvin wrote:
> > Hi Hoon,
> >
> > Using a reference value is not always a good idea, because experimental
> > effects can play a role.
>
> I want to elaborate a bit on this point in Scott's post, particularly
> given the nature of your sample.
>
> The materials in a battery, as they charge or discharge, can undergo
> changes in morphology. Morphology can have an impact on the measured
> amplitude. More specifically, inhomogeneity in the sample -- pinholes,
> for instance -- have a known effect on the amplitude. See, for example:
>
> http://dx.doi.org/10.1103/PhysRevB.23.3781
> http://dx.doi.org/10.1016/0167-5087(83)90730-5
> http://gbxafs.iit.edu/training/thickness_effects.pdf
>
> My point is that you may need to question the assumption that S02 even
> should be transferable in your measurement.
>
> B
>
>
> > BUT, S02 should not change during charge-discharge on a single sample,
> > or a series of samples prepared and measured similarly. Instead, it's
> > likely something correlated with S02 in the fit is changing, and so the
> > fitting routine is getting a bit confused and attributing part of the
> > change to S02. (That's not a knock on the fitting routine; it doesn't
> > know any better unless you tell it!)
> >
> > I think the best recommendation is to do a simultaneous fit on multiple
> > spectra, constraining the S02 to be the same for each. So you're still
> > fitting S02, but forcing all the spectra to use the same value.
> >
> > Second best is to fit one spectrum and allow S02 to vary, and then
> > constrain all the other fits to use that value.
> >
> > --Scott Calvin
> > Sarah Lawrence College
> >
> > On Sep 18, 2014, at 7:06 AM, HOON Kim <science@live.co.kr
> > <mailto:science@live.co.kr>> wrote:
> >
> >> Hello,
> >>
> >> I am a bit confused about the amplitude reduction factor (S0^2), in a
> >> sense that whether this factor must be determined by fitting or
> >> constrained by a reference value for a specific element. I'm dealing
> >> with a cathode composite (for lithium-ion battery) comprised of two
> >> crystal phases. During charge-discharge, the amplitude reduction
> >> factor changes and at a certain state of charge (SOC) it changes a lot
> >> such as from 0.77 to 0.67. My understanding is that it may reflect
> >> the phase transition of the material into the amplitude reduction
> >> factor. But, I'm not sure ... I need advice on this.
> >>
> >> Thank you !
> >>
> >> Kind Regards,
> >> HOON
> >> _______
> >
> >
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> >
>
>
> --
> 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://bruceravel.github.io/home/
> Software: https://github.com/bruceravel
> Demeter: http://bruceravel.github.io/demeter/
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