I am trying to fit a Nyquist plot of polymer membranes. How can I fit the data? How do I know that the fit is good or not (other than by looking at the fit)?
You can try ZView to fit your data. To determine the "goodness" of your fit please realize that the fitting should support an underlying physical model. Of course, one can fit anything - but it usually has nothing to do with the physical reality.
Kind regards
Peter
Thank you Peter Wagner for the suggestion. I am currently using ' ZSimpWin' software. When I fit the data (obtained from CH instruments, USA), the fit dont matches well to the physical data. So when can I reject/ accept a fit by looking at the error and Chi values. What is the acceptable error limit. Could you please comment.
thanks and kind regards
I cannot comment on any fit without looking at the data, the used model etc. In our case we obtain very low errors, but it is still a big discussion whether our underlying model can be related to the physical reality.
Kind regards
Peter
I fitted the impedance data (attached) obtained for Nafion using Zview. I tried the model R(R-CPE)(R-CPE) (attached). The resistances obtained are Rs 1799, R1 995.1, and R2 6775. How do I check whether the results are good or bad? Is it a good fit (snapshot attached). Which R should I consider as the one for Nafion? Is it Rs or a combination of Rs, R1 and R2.
Sorry for asking too many questions.
Thank you for your time and patience.
Yes, Zview is a choice. You also can download and install Autolab software, which includes FRA (Frequency Response Analysis) program, it can be used to fit Nyquist plot following any model you think.
I am afraid I will still not be able to answer your questions. Experimental setup to determine the EIS data? Do you want to determine the membrane resistance from your measurement?
And by the way: A parameter setting of 1.0 for a CPE seems to be quite uncommon to me. In our EIS fits we usually use values less than 1 to account for the nonlinearity of the circuit.
But as I said I can just speculate. I recommend to discuss your results with your supervisor.
Kind regards
Peter
ZView is quite uncomfiortable. If you want something nice, fast, importable/exportable with ease, try EC-Lab, from Bio-Logic. They have a demo version that has some examples of data. You can easily import data obtained from software of other brands, as well as import text files with the EIS data. You can use plenty of different pre-built circuits as well as propose your own.
Yet, be aware that you should not construct your equivalente circuit without good knowledge of the system and a rational explanation for your choice.
With respect to the previous comment, setting the alpha parameter of a CPE to 1 only means you are modeling with a pure capacitor, nothing else.
For fititng the R values, all R values can be estimated from the Nyquist plot itself, the magnitude should not be a problem, it is more the validity of your circuit to explain your data which poses an issue. Do you have a physical explaination for it?
I recommend you reading our paper in Chem Soc Rev from 2012, as well as the Impedance book of Bernard Tribollet and Mark Orazem, which is quite didactic.
Kind regards
Xochitl
Hi Xochitl
thank you for the comments and suggesting the review..
Hi Akhil,
Have a look also at a free impedance data fitting programme named LEVMW authored by J. R. Macdonald and freely available at .
Best,
Antonio F. Fuentes
@Antonio
Dear sir
Please see this question and if you can help me in this.
https://www.researchgate.net/post/How_to_fit_complex_relative_permittivity_with_Havriliak_Negami_dispersion_function_and_low_frequency_conductivity_term_using_LEVMW_software
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