A dielectric relaxation is usually modelled with a resistor and a capacitor in parallel to each other (RC element). If you have several relaxations, you should use several RC elements in series to each other. In almost all cases the impedance data from a real sample cannot be modelled very well by ideal resistors and capacitors. Therefore, you can replace the ideal capacitors with a CPE. In some rare cases you can also use a CPE in parallel to the ideal resistor and capacitor. This is possibly only for intrinsic bulk relaxations in ceramic materials.
A dielectric relaxation is usually modelled with a resistor and a capacitor in parallel to each other (RC element). If you have several relaxations, you should use several RC elements in series to each other. In almost all cases the impedance data from a real sample cannot be modelled very well by ideal resistors and capacitors. Therefore, you can replace the ideal capacitors with a CPE. In some rare cases you can also use a CPE in parallel to the ideal resistor and capacitor. This is possibly only for intrinsic bulk relaxations in ceramic materials.
Yes, CPE represents the imperfection of the standard element (capacitor). In the formula for the impendance of the constatnt phase element (Z=1/[Q(iw)^a; w- is the ac frequency) there is a nonideality factor "a". When a=1, the CPE element resembles an ideal capacitor, when a->0 then the element adopts the characteristics of an ideal resistor, and when a-> -1 then CPE element is similar to an ideal inducator.
Thank you one and all,
can you please suggest me some good reading literature for analyzing the impedance data?
Depending on what kind of samples you are measuring you might be interested in this work:
Impedance Spectroscopy of Electroceramics
R Schmidt
New York, 01/2007; ISBN: 978-1-60021-769-2 In book: Ceramic Materials Research Trends, Publisher: Nova Science Publishers, Editors: P.B. Lin, pp.325-355
You can download a copy from my researcher profile if you like.
Possible, my paper can help you. Interpretation of the impedance comprising negative capacitance and constant phase elements on iron electrode in weakly acidic media
V. V. Elkin, A. I. Marshakov, A. A. Rybkina, M. A. Maleeva
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