I suggest you to use a software as Zplot..

Usually the resistance is determined  intercept of the high frequency part. I don't know which kind of cell are you studying. For example if it is a symmetric cell and you want to study the electrochemical performance of the electrolyte, the Nyquist plots give you informations about distinct processes. Your plot seems "something" recorded at high temperature. If it is an electrolyte (I think yes!!!)  I think that it is the contribution of electrode interface. If it is related to a single cell I think that you have an high mass tranfer resistance, maybe due to the electrolyte losses. It's not clear. You need to specify some informations to obtain a good answer. Any way you need to  fit the data with an ideal circuit. It can ''build'' with the software.

About the ionic conductivity you need other informations as the geometry of the electrode, the internal resistance etc... Do you need the total ionic conductivity? Consider that the electrolytes have the grain boundary and the bulk conductivity (not in your plot). So...it's an hard work without any information.

Best regards

Grazia

as Grazia Accardo, for 1)Resistance(s) and 2)capacitance. Also, for ionic conductivity we suggest to extent more the part of the lower frequency-f regime, if possible (0.01Hz

@Grazia maam: Thank you for your answer. My sample is CeO2 as electrolyte and platinum was coated as electrode. The graph is at 400 C. Please elaborate what shall i do next.

It's strange because around 400°C you should see three different contribution, bulk, grain boundary and electrode. Plot your data with the ideal circuit R (RC)(RC) and calculate the internal resistance.then if you have the area of electrolyte you can calculate  the conductivity I can send you zplot if you want. 

@Grazia maam...it shall be very kind of you for providing zplot.

email : [email protected]

I will send you!!! Read this file, it can help you

Bhasker,

I am no expert. I am still trying to figure out many details of EIS. But from what I understand, resistance you get it from the diameter of the semicircle, capacitance  from the characteristic frequency (frequency of the top of semicircle), and for ionic conductivity you need previous knowledge or guess which ions the material conducts. then to figure out a way to block electrons and allow only the ions you want to measure, for example using a concentration cell. 

Are you using a Solartron 1260? I use that one and it shows the discontinuities like your spectrum. I use another fitting software and never been able to make appropriate fit. Can I get a copy of Zplot as well if you have a chance?

Good luck!

Chek your email box. You will find the software.

Good luck

Grazia

Dear Soni..

Your Nyquist plot was not nice. In the low frequency region, i see some inductance effect. It was due to the connection probe problem. please check that... 

The plot shows two overlapped semicircle region. High frequency is related to grain and low frequency is related ti grain boundary. spike region was not observed. without spike, you cannot manually find the resistance. so the only option is Z-view or Z-simpwin software.

@Heber Martinez : please share your email id.

[email protected]

Thanks!

Dear Bhasker, 

I have (too) many problems seeing such a low quality IS spectrum...

definitely your measurement setup was wrong: too short integration time etc, also, selection of automatic ranges was wrong as clearly, you have some discontinuities in the spectra. there are several such discontinuities that I am pretty sure are due to the hardware/Solartron misuse.

I cannot see any inductance at low f, as the data does not cross the x axis... but it is also strange that it is not seen at f>10E5 (edit: maybe at 400C it should not, I did not read properly whole discussion).

I would say, this data is not suitable for any fitting. In my opinion you have to redo the experiment. and understand how the Solartron, which is an amazing device by the way.

Spectra of CeO2 with Pt electrodes should look differently at 400C with more clearly distiguishable semicircles. You can always take literature data and try to simulate it just in case.

Best regards,

Sebastian 

Dear Bhasker,

The Impedance graph clearly indicates a problem with the measuring system. With Solartron systems I had to sent these back for service to England, after which they worked fine again. I have had similar issues with other FRA-systems. It is always good to have a test circuit (dummy)  to check whether the system performs well. Another added point may be insufficient shielding or proper grounding. A good method to check (validate) your data before doing an analysis is the Kramers-Kronig test. A free program is available from:

www.utwente.nl/tnw/ims/publication/downloads/KK-windows.zip (with brief manual)

Best regards,

Bernard A. Boukamp

as Sebastian Molin,  you might have to redo the experiment.  Also, in my opinion there are initial indications for electrodes' modifications (faster at higher temperature scans). Which materials do you use as electrodes ?

Hello Bhasker,

from my experience I know that Solartron is relatively slow device. For measurement of your spectrum you need maybe 5 minutes. Further point, the temperature around 400°C in the air is really hard to get stable during these 5 minutes. Use you some PID-Regulator, so you get high oscillations in a wide range. Your sample may be very sensitive in respect to temperature oscillations. These temperature oscillations are reflected in your impedance graph in low frequncy range. You will see it better in the Bode-plot (or ReZ vs Freq).

Have you got no such oscillations at room temperature, so you need not to repair your Solartron device. I suggest an upgrade for the temperature controller to the master-slave-PID-system and optimize it. 

Best Regards,

Vladimir

PS By the way, the measurements made under unstable conditions are useless.

Dear Bhasker,

As stated above,the shifts in your impedance diagram clearly come from issues with the Solartron device. Sometimes (most of the time actually) it arises when one of the wire of the Solartron is damaged. If by chance you have spare wires, try to replace them first before sending the device for service.

And I agree that the temperature of your CeO2 pellet was not stable. It explains the "snail-like" shape at lower frequency.

Best Regards

Aurélien.