[Ifeffit] Inconsistency of the amplitude reduction factor

[HOON Kim]

Dear Bruce,
Thank you for the references. 
In my opinion, it is a bit tricky to say that the battery cathode undergoes a morphological change during a single charge. There is apparently a phase transition including crystal lattice changes and oxidation state changes. If the change of the crystal structure is remarkable (e.g. layered structure to spinel structure), this may lead to the morphological change. My feeling is that even a normal phase transition may affect the 'amplitude reduction factor' during the electrochemical cycling. 
Kind Regards,HOON


> Date: Thu, 18 Sep 2014 09:04:17 -0400
> From: bravel at bnl.gov
> To: ifeffit at 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 at live.co.kr
> > <mailto:science at 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 at bnl.gov
> 
>   National Institute of Standards and Technology
>   Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
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>   Upton NY, 11973
> 
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