[Ifeffit] Inconsistency of the amplitude reduction factor

HOON Kim science at live.co.kr
Thu Sep 18 07:20:06 CDT 2014

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 0.77At 20% charge, it was 0.6740% charge = 0.6660% charge = 0.6380% charge = 0.68full 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
To: 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 CalvinSarah Lawrence College
On Sep 18, 2014, at 7:06 AM, HOON Kim <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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