i am trying to do some EIS measurements for my ceramic coatings but the nyquist plot i get at the high frequency region i.e at the beginning of the plot is more like a hook shaped rather than a semi circle. Can anybody tell what may be the cause of getting this kind of plot? Please see the attached image.
Dr. Rahman,
In my view, at higher frequency a hook shaped plot is nothing rather than 450 Warburg type line due to diffusion control (depends on perturbation frequency) i.e. Warburg impedance controlled by the counter-ions into the ceramic coating. After that at low frequency film behaves as simple capacitor and the plot becomes almost vertical.
With regards.
It seems you can only consider the negative imaginary portion of the diagram. Positive imaginary data ("high-frequency hook") are likely to be spurious contributions from your measuring setup. You should indicate some frequencies in Nyquist plots.
Mr Fabio Coral Fonseca,
thanks for your answer the freq range for the full plot is 100KHz to 100mHz, and for the negative portion(hook) the frequency range is 100kHz to3.5kHz.
As I see, -Im(Z) is changing the sign at high frequencies. It means that stray inductance (L) is expressed at these frequencies and dominates over capacitive nature of interface phenomena.
Z =R+jwL+1/(jwC) = R +jwL -j/(wC) = R+j(wL-1/(wC)). It is clear from this simplified presentation that "inductive" (positive) portion of the imaginary part will increase with frequency.
This is probably due to your measuring setup, electrical leads, for instance. You may wreath the cables leading to the sample to suppress this effect, or to include L in your fitting model, but you have to be cautious, since fitting models can easily lead to misinterpretation of experimental results. Some impedance analyzers have an option to calibrate the device prior to measurement in order to eliminate the influence of measuring setup on EIS analysis of your sample.
That shape is typicall of inductive behaviour that can be related to the sample or/ and to the experimental set up (wires and the measurment configuration). You can correct the open / short circuit previous to the measurment or take into account the in-series inductive part in the equivalent circuit fitting model. This is a typical problem in EIS.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Ceramics