[Ifeffit] Inconsistency of the amplitude reduction factor
bravel at bnl.gov
Thu Sep 18 08:04:17 CDT 2014
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:
My point is that you may need to question the assumption that S02 even
should be transferable in your measurement.
> 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:
>> 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,
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
Bruce Ravel ------------------------------------ bravel at bnl.gov
National Institute of Standards and Technology
Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2
Upton NY, 11973
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