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 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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