"Voigt Circuit" which is a series combination of Voigt elements (i.e. parallel RC's), is commonly used for Kramers-Kronig relations checking; and as I imagine it is generally believed to be able to be fitted to various electrochemical impedance spectra? Is this belief true or not? And if the answer is "Yes", is there any theoretical basis for that or it is only a practical sense (I mean that it is approved according to fitting results of experimental data to Voigt circuit)?

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It is known that an electrochemical impedance spectra can be modelized with series-parallel combination of resistors and capacitors elements. What is more, for a given impedance spectra they are an infinity of different combinations of R-C elements which accurately model the same complex impedance.

Similar observations are commonly done in the field of imperfect dielectrics (non-Debye) for the complex permittivity spectra.

For examples: pages 10-11 , page 16 and pp.27-32 in the paper https://fr.scribd.com/doc/71923015/The-Phasance-Concept . Each example of complex impedance is modeled with several different networks of R-C elements.

On theoretical viewpoint, all this is related to the energy efficiency of the phenomena in the experimental system, that is the presence of dissipative components (R) and storage components (C) distributed on various manner. Even if the energy storage and energy dissipation are respectively on different physical nature in different experimental devices, possibly in some cases the complex impedance is likely to be similar due to a similar global energy efficiency behaviour. So, an infinity of different R-C models are likely to be derived.

This can be observed not only in experiments but also in purely theoretical studies for very simplified geometrical configuration : https://fr.scribd.com/doc/23155389/Theoretical-Impedance-of-Capacitive-Electrodes

In addition. To go beyond the question raised, the following quotation is extract from the first paper quoted above :

It has long been recognized that many impedance loci result in well-defined semi-circles with center depressed below the real axis. Linear loci are also commonly observed associated to rough electrode surface, porous electrode, diffusion, etc. "This features mean only that the system includes some part(s) transferring energy with constant efficiency in a range of frequencies. Any affirmation of the nature and mechanisms of the phenomena involved would be pure hypothesis if only based on impedance analysis."

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