There are several issues to answer your question. First, is your sample a coated sample or a bare sample ?? Second, Bode curves (Bode-Z & Bode-phase) are needed to answer your question. What it looks like is that your sample is coated.

If possible, indicate the type of sample and the type of coating (if applicable).

Hi,

have a look at

https://www.biologic.net/topics/nyquist-plots-why-use-the-orthonormal-scale/

https://www.biologic.net/documents/studying-batteries-with-electrochemical-impedance-spectroscopy-electrochemistry-battery/

In this curve, first, there is a semicircle that corresponds to the substrate, then the Warburg impedance phenomenon occurs, that is, when the diffusion of species into the coating porosity is less than the charge transfer processes, the low-frequency diffusion in the Nyquist diagram at an angle of 45 ° Is displayed. At low frequencies, the slope of the Bode-Z diagram reaches -1/2 while the Bode-Phase diagram tends to 45 °.

It's better to upload the bode curves.

Hi s. o. ! What kind of system are you studying? If is an electode/electrolyte interface, then it seems to me that maybe you are using a to high frequency. Normally, at high frequency limits (f>10 kHz) anomalous responses, as the one you are showing, are obtained. Conventionally, the response that you are obtaining is not related to your system, but to your equipment set-up. Try to measured it again, but using a frequency range between 10 kHz and 10 mHz.

Best wishes!