I made sintered electrolyte pellet and coated it with platinum using DC sputtering. I measured impedance graph (in range of 500-700 C) using EIS. How shall I proceed for its analysis. How do I measure ionic conductivity ?
You can try with equivalent circuit fitting - use the same fitting model for all spectra. This will seprate the resistance in different components, for example interfacial, bulk, ohmic etc... After the extraction of the fitting parameters (R, CPE, etc...) you can plot the different resistance components in Arrhenius coordinates [Log(R) vs 1/T].
Alternatively you can use Differential Impedance Analysis (check the works of Stoynov and Vladikova).
Z-plot is probably your best software for fitting. however, with ac impedance, you always need to be confident that there is a real physical process or structure that is being modelled by each component and that the component values that your model gives you are reasonable. You can fit any data with a model that has 4 or 5 free parameters: reality checking is essential. E.g. for a polished metal electrode in 1 M KCl, we might expect an interfacial capacitance of around 20-50 uF/ cm^2 and a solution resistance of the order of ohms. If your data are orders of magnitude out, you've probably got the wrong model circuit, which is distressingly easy to do.
For the very beginning in EIS, I would suggest to observe the results visually in the representation of Im(Z) vs. Re(Z). In these graph you will be able to find a semicircle or maybe two. Depending on temperature, sometimes you will be able to see only a part of semicircle. The diameter of the semicircle is equal to resistance R, and the conductivity sigma=d/(R*S), where d is the thickness of your pellet, S is the surface area of the electrode.
This method is not exact, but it is a good way to learn. After you can proceed with fitting and compare your results.
Literature: J. Ross Macdonald, Impedance Spectroscopy, 2005 (second edition), Willey.
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