Understanding the validity of impedance and modulus spectroscopy on exploring electrical heterogeneity in dielectric ceramics

Abstract

Combined modulus and impedance spectra are widely employed to explore electrical inhomogeneity and carriers' behaviors in dielectric ceramics based on equivalent circuit. However, discrepancies are found between practical dielectric responses and widely proposed equivalent circuits. Taking ZnO varistor ceramics as an example, a low-frequency dielectric relaxation, which can be detected in practical dielectric spectroscopy, is overlooked in simulated dielectric spectroscopy based on the proposed equivalent circuit according to modulus and impedance spectra. Therefore, equivalent circuits are frequently incomplete because the real low-frequency dielectric response is unable to be characterized from them. The problem originates from debatable understanding of frequency responses in modulus and impedance spectra. The low-frequency peak in modulus spectroscopy is proved originating from DC conductance instead of a real dielectric relaxation and the involvement of DC conductance component makes a low-frequency dielectric relaxation unable to be characterized in modulus spectroscopy. Therefore, improved dielectric spectroscopy eliminating the component of DC conductance is proposed and a clear peak corresponding to the low-frequency dielectric relaxation appears. In addition, a modified equivalent circuit which is in accordance with practical dielectric responses in not only modulus and impedance spectra but also dielectric spectroscopy is presented.

Grain boundary engineering that induces ultrahigh permittivity and decreased dielectric loss in CdCu3Ti4O12 ceramics

“…Two responses can be observed in Z ′‐ f , which are denoted as the contributions from the grain boundaries at low frequencies and the grain/bulk at high frequencies. Only one response can be seen in Z ″‐ f , which is referred to as the grain boundary response due to the limits of the measurement processes . Impedance spectroscopy is a useful tool to analyze the resistivity and conductivity when long‐range conduction dominates because it provides information about the element with the elevated resistance.…”

“…The temperature dependence of DC conductivity can be analyzed by the Arrhenius law, which is expressed as follows where E ca is the activation energy of electrical conduction, and T is the absolute temperature.…”

“…A linear fitting of ln σ dc vs 1000/ T is displayed in Figure for (D) x = 0.00, and (E) x = 0.08. The result gives the E ca values for the different CdCu 3− x Zn x Ti 4 O 12 ceramics for x = 0.00, 0.01, 0.02, 0.04, 0.06, 0.08, and 0.10, and the associated values are 0.76 ± 0.02, 0.77 ± 0.02, 0.76 ± 0.02, 0.79 ± 0.01, 0.82 ± 0.01, 0.83 ± 0.02 and 0.79 ± 0.02 eV, respectively, which are comparable to E gb , implying that the electron hopping process is easily activated, and that the electric response of CdCu 3− x Zn x Ti 4 O 12 ceramics should be attributed to the contributions of the bivalent ionized oxygen vacancies related to the grain boundaries . Figure displays the value of E ca as a function of Zn content.…”

“…Only one response can be seen in Z″-f, which is referred to as the grain boundary response due to the limits of the measurement processes. [39][40][41][42] Impedance spectroscopy is a useful tool to analyze the resistivity and conductivity when long-range conduction dominates because it provides information about the element with the elevated resistance. Therefore, it is easy to conclude that the R gb of CdZn x Cu 3−x Ti 4 O 12 ceramics is enhanced by Zn doping, as shown in Figure 5D.…”

“…Since the electrical conduction of ACTO ceramics follows a field-assisted thermionic emission process across the Schottky barrier at high temperature, 34,42,[49][50][51] the barrier height at grain boundaries Φ gb can then be evaluated by the activation energy of electric conduction E gb . Figure 6D displays the value of E gb as a function of Zn content.…”