Impedance and Dielectric Spectroscopy of Functional Materials: A Critical Evaluation of the Two Techniques

Abstract

Impedance and dielectric spectroscopies are closely-related techniques for measuring electrical properties of materials. The techniques differ in two ways. First, impedance measurements are usually made over several decades of frequency (ie broadband) whereas most dielectric measurements are made at fixed frequency. Second, time constants that control semicircles in impedance complex plane plots and peaks in permittivity or tan δ spectroscopic plots are not the same. In impedance data, time constants represent conducting components and parallel resistance-capacitance (RC) combinations; in permittivity data they represent dielectric processes and series RC combinations. Differences between the techniques are confined to data analysis procedures and interpretation. Using broadband data, it is possible to (i) determine the best equivalent circuit to fit experimental data, (ii) unambiguously evaluate and assign resistance, capacitance and time constant parameters to regions of the material being measured and (iii) quantify departures from ideality using constant phase elements, CPEs. The advantages of using broadband measurements are highlighted with two examples: calcium copper titanate, CCTO which is often, erroneously, described as a giant or colossal dielectric; lead magnesium niobate, PMN, the classic relaxor ferroelectric whose characteristic properties are controlled entirely by the presence of non-ideality, represented by a CPE, in its equivalent circuit.

Effect of iron acceptor doping and calcium donor doping in potassium sodium niobate‐based lead‐free piezoceramics

“…Accordingly, impedance spectroscopy can be used to separate conductive and dielectric contributions. In this way, extracting resistive and capacitive contributions gives us more details on the electrical processes involved 69 …”

“…Accordingly, impedance spectroscopy can be used to separate conductive and dielectric In this way, extracting resistive and capacitive contributions gives us more details on the electrical processes involved. 69 In our study, we conducted impedance spectroscopy on all KNN samples. The Nyquist plots, which depict the imaginary part versus the real part of the impedance (Z″-Z′), for both undoped KNN and doped KNN are illustrated in Figure 4.…”

Impacts of diffusive ion migration on ferroelectric properties in BaTiO3 composite

“…The fitted circuits consist of the resistance (R), capacitance (C), and the constant phase element (Q). It has been observed that the bulk properties of many conducting materials are best represented by the addition of a constant phase element (Q) in parallel with R and C [56]. The presence of Q can be attributed to the deviation of the impedance response from the ideal Debye relaxation behavior [57].…”