I did scanning impedance experiment in wet-state and obtained a bode plot ( a graph of a frequency response of the gel). I want to separate Z' and Z" to draw a Nyquist plot.
If you have bode plot, say Impedance (Z) vs frequency and Phase angle (theta) vs frequency, then you can calculate:
Re(Z) = Z cos(theta)
Im (Z) = Z sin(theta)
Now just plot Im(Z) vs Re(Z). You will get Nyquist plot. A common practice is to plot |im(Z)| vs Re (Z) in material characterization as the imaginary part because of capacitive contribution is negative.
Thanks Christian Punckt for your reply. However, I didn't find it very friendly. Anyone can be new to a field and that's because I've asked a basic question! I was trying to find an electrochemist to explain this to me to ask more questions.
Actually, I searched google a lot and couldn't find what I was exactly looking for. Because electrochemistry is not my background and as a result there were many terms that I couldn't understand while reading. And understanding all of those terms essentially was taking a lot of time from me for a side work. I think researchgate is somewhere that you can discuss with other researchers even if your question is very basic and easy (may be not for everyone).
Thanks Gyanendra Bhattarai for your answer. It was very useful and accurate. And as far as I found ( from different sources ) the slope of the Nyquist plot is suggesting the phase shift between real and imaginary components. In consequence, we can find a model that the material is behaving such that.
I've another question. If I understand correctly, the impedance magnitude (ohm) that we have on y-axis is a combination of resistivity and capacitance. if you look at two attached files, I've done the impedance spectroscopy and drawn the bode plot for wet and semi-wet chitosan gel to compare the ionic conductivity between those. As you can see the impedance magnitude is reducing as the gel is becoming dehydrated. This is sth I can't understand. Can you explain why this happens? I assume that the impedance should increase, so we obtain lower conductivity....
If you have Impedance (magnitude) and Phase angle data (not image), then converting these to Nyquist or complex capacitance plot could be useful to see what is happenning. Can you upload or send the data in message?
I am not sure if I have heard the usefulness of slope of Nyquist Plot. But If you draw a vector from origin to any point on the Nyquist Plot, the angle made by the vector is the phase difference between the input current and output voltage at that particular frequency but it is not the phase difference between real and imaginary parts (because the phase shift between real and imaginary part is always +/- 90 degrees.)
I don't have much understanding in Chemistry however, I see two things that I can guess!
1. Dehydration is increasing the concentration of your gel. upto a certain concentration, the ionic conductivity increases. Am I right? So, you might be in the regime where the ionic conductivity is still increasing.
2. Dehydration decreases your water content and since water has high dielectric constant, the capacitance decreas with dehydration and causes the impedance to increase as you have expceted. (but not seen in graphs)
However, I am not sure/ or I can say, I don't know, which contribution dominates in your regime.
Hi Azadeh
I am dealing with the same problem and my supervisor just suggested me this paper about EIS which explains things step by step.
Hope you find it useful.
http://webcache.googleusercontent.com/search?q=cache:fDWLngjtAQwJ:www.solartronanalytical.com/download/Technote-26-Analysis-and-Interpretation-of-EIS-Data-for-Metals-and-Alloys.pdf+&cd=5&hl=en&ct=clnk&gl=au
Dear Mr. Sarvghad,
The link is not working. Can you please repost the link?
It can be calculated from impedance and phase by using the following relation
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