The Interpretation of Non-Ideal Dielectric Admittance and Impedance Diagrams

Abstract

It is well known that many dielectric materials such as ionically conducting ceramics show complex susceptibility (Cole-Cole) plots which are non-ideal, i.e. which depart seriously from the ideal semi-circular form. It is also known that similar departures may be found in the corresponding impedance or Z-plots and admittance or Y-plots. The commonly accepted interpretation of skewed circular arcs and spurs in the Y and Z representations relies on the concept of Warburg impedance which is based on the assumption of a diffusive model for the system. However, the Warburg impedance can only explain circular arcs and spurs inclined at an angle π/4 to the normal, while the available experimental data show clearly a wide range of angles in which the unit slope angle represents only a particular case. The present paper suggests that a more plausible interpretation may be possible which includes the whole observed range of behaviour and which makes use of the concept of „non-Debye capacitance”︁ having a frequency-independent ratio of the imaginary to the real parts of the complex dielectric susceptibility. Such non-Debye properties are generally found in most solid dielectric materials and a simple physical model has been proposed to explain this almost universal behaviour. A discussion is given of the application of this concept to the interpretation of a wide range of complex Z- and Y-plots giving a simple and physically plausible explanation of the observed behaviour.