Calculating conductivity from Nyquist plot, plot has no semi-circles?

I am familiar with the following process for calculating conductivity from a Nyquist plot:


1. Run impedance on potentiostat
2. Plot - Imaginary Z vs Z
3. Generate equivalent circuit
4. Fit data
5. Calculate conductivity by entering the resistance value, thickness, and diameter of sample


My confusion is that, in the past, my spectra always had a semicircle. Now I am running samples which are giving basically a 45 degree line that starts to the right of 0 on the X axis. I believe I have an equivalent circuit (Resistor + Constant Phase Element/Resistor + Warburg element). My question is, are you able to calculate conductivity as long as you can extrapolate the resistance? In other words, if you have an equivalent circuit which contains a resistor, can you always calculate the conductivity? Or do you need a semi-circle? Thanks.


