[Ifeffit] Inconsistency of the amplitude reduction factor

[Scott Calvin]

By the way, you should also look closely at how well the edge jump is being determined by Athena (or whatever software you use for the data reduction). If there's a white line or pre-edge feature that's changing, it's possible the default behavior of Athena is not determining the edge jump in a consistent manner. That would directly lead to an apparent change in S02. The solution in that case is to adjust the parameters in Athena to assure the edge jump is determined in a consistent fashion.

--Scott Calvin
Sarah Lawrence College

On Sep 18, 2014, at 8:20 AM, HOON Kim <science at live.co.kr<mailto:science at live.co.kr>> wrote:

Dear Scott,

Thank you for your advice.

Q) I assume that your second solution allow different S02 values for each spectrum?

I'd like to be more specific about my obtained results,

At reference state (that means without any applied current), the amplitude reduction factor was 0.77
At 20% charge, it was 0.67
40% charge = 0.66
60% charge = 0.63
80% charge = 0.68
full charge = 0.67

Most of the fitting parameters were reasonable and the result well corroborates with previous study (papers) from other group (but I'm not sure about the value of the amplitude reduction factor as there were little information about it).

Kind Regards,
HOON

________________________________
From: scalvin at sarahlawrence.edu<mailto:scalvin at sarahlawrence.edu>
To: ifeffit at millenia.cars.aps.anl.gov<mailto:ifeffit at millenia.cars.aps.anl.gov>
Date: Thu, 18 Sep 2014 07:23:53 -0400
Subject: Re: [Ifeffit] Inconsistency of the amplitude reduction factor

Hi Hoon,

Using a reference value is not always a good idea, because experimental effects can play a role.

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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