Impedance spectroscopy measurement was carried out for dry solid porous specimen with high DC resistivity (rho) = low DC conductivity (sigma) and enclosed graphs were prepared. Electrodes are made of conductive graphite paste painted on 2 lateral sides of specimen.
Is it possible to express in the right way DC electrical conductivity/resistivity of material?
Can it be read out from Cole plot? Real part of Z (where imaginary is "equal 0"), then calculation of resistivity? Which part can be assigned to the sample volume property (it seems, there are three semicircles)?
I would appreciate any info or references to the literture dealing with impedance spectroscopy of porous solid materials.
Thanks in advance.
1- yes of course, it is possible to express the conductivity or resistivity in porous materials
2- it is observable in the cole-cole spectrum: the increase in resistivity a function of temperature
3- you have, in the spectrum Z '' = f (Z ') three half-circles which can be attributed to the conduction of the grain, the grain of the gasket and éléctode son or conductors, respectively.
Dear Dr.Fiala, did you make your measurements in vacuum? If not, there is always a possibility of moisture absorption in porous samples. Moisture may appriaciably affect electrical conductivity. If you are interested in d.c. conductivity, it is better that you measure current by applying d.c. voltage in presence of vacuum.
Dear Dr. Kumar. Measurements were carried out on concrete samples (porosity about 5-10 vol. %) in laboratory conditions (20°C, RH 40-45%). There could be some non-significant amount of water due to water vapour adsorption (could be determined by gravimetric method/sorption isotherm, but it was not taken into account). I expected it would not affect IS measurement significantly.
I want to compare resistivity/conductivity of material resulted by using both methods - DC and IS measurements. In case of this type of materials, DC seems to be problematic (high resistance of material, electrode polarization, transition resistances).
M. Hamdi - Which intersection (enclosed graph) could be connected to material resistivity (calculated from Z' where Z''=0)? The yellow (right intersection) or the blue one? I expect the green line (right intersection) is significant for contacts (electrode-specimen). Am I right?
Dear Dr. Fiala
You have to mount your samples in a metallic sample holder with vacuum inside for electromagnetic shielding even if moisture effect is not there as you are dealing with very high resistance.
Definitively do not use DC because you will compute in your measured resistance the charge transfer at the electrodes. The problem has already been addressed in literature, please read http://dx.doi.org/10.1016/S0958-9465(02)00053-7
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