Reinvestigation of conducting properties of Ca-doped barium titanate

Relaxation processes of Ba1−xCaxTiO3 ceramics with x = 0.05, 0.10 and 0.23 Ca contents were studied by combining the dielectric modulus and complex impedance experiments. Use of both methods permits an exploration of relaxation processes in both time and frequency domains, including relaxation distribution function at low and high frequency relaxation regions (grain and grain boundary). From an analysis using the complex impedance formalism, the predominant time distribution relaxation function turns out to be a Cole-Cole type, whereas from the dielectric modulus formalism it is described by non-Debye relaxation functions. While activation energies derived from the dielectric modulus formalism are characteristic of doubly-ionized oxygen vacancies (0.85–1.00 eV), they are from the complex impedance approach expressed as a typical electronic conduction (1.2–1.5 eV). It was identified that the impedance formalism describes well the relaxation in the low frequency regime with similar activation energy derived from the Jonscher power law (1.1–1.4 eV). The present study highlights the potential of using both impedance and dielectric modulus formalisms to identify and quantify non-Debye relaxation process and conducting properties in mixed electronic-ionic conductors.