Complex impedance spectroscopy of perovskite microwave dielectric ceramics with high dielectric constant

Abstract

The AC impedance of SrTiO3, Ca0.9Sr0.1TiO3, Ca0.7Sm0.2TiO3, and Ca0.7Sm0.3Ti0.7Al0.3O3 microwave dielectric ceramics with perovskite structures has been analyzed. The impedance spectroscopy results reveal the electrical properties of this series of samples vary significantly with the ceramic microstructure and electrical homogeneity. The εr values of grains for SrTiO3 and Ca0.9Sr0.1TiO3 ceramics are 193.8 and 138.1, respectively, confirming that dielectric response of the high‐εr microwave ceramics is contributed to the grains, at microwave frequencies. Impedance spectroscopy of Ca0.7Sm0.2TiO3 ceramic illustrates that electrical heterogeneous microstructures include interior grains and grain shells. The secondary phase existing in Ca0.7Sm0.2TiO3 ceramic causes deviation in bulk permittivity, resulting in a higher εr ~ 148 of grains than εr ~ 112 of bulk permittivity, measured at microwave frequencies. Grain and grain‐boundary impedance of Ca0.7Sm0.3Ti0.7Al0.3O3 ceramic cannot be separated completely. The permittivities of grains and grain boundaries in Ca0.7Sm0.3Ti0.7Al0.3O3 ceramic are εg ~ 17.8 and εgb ~ 20.8, and the combination of them is close to εr ~ 40 at microwave frequencies. The LogI−LogU curves of the ceramic system indicate that the conducting mechanism of grains and grain boundaries follows ohmic behavior.

Enhanced photovoltaic performance via polarization in Bi/Co co‐doped KN‐based ferroelectric ceramics

“…The complex impedance spectrum of the 0.98KN–0.02BC sample at 500°C with various DC biases is shown in Figure 8D. With increasing voltage, the impedance radius slightly observed, indicating an increase in conductivity due to the applied DC bias 56 . The substitution of Co ions for Nb ions and Bi for K ions is balanced in KNbO 3 –BiCoO 3 , but considering the valence conversion behavior of Co ions (Equation ), BiCoO 3 doping of KNbO 3 can be considered acceptor‐doped, as represented by the following equation: $$\begin{equation}{V}_{{\rm{\ddot{o}}}} + \frac{1}{2}{{\rm{O}}}_2 \to {\rm{O}}_{\rm{O}}^x + 2{{\rm{h}}}^ \bullet \end{equation}$$…”

“…With increasing voltage, the impedance radius slightly observed, indicating an increase in conductivity due to the applied DC bias. 56 The substitution of Co ions for Nb ions and Bi for K ions is balanced in KNbO 3 -BiCoO 3 , but considering the valence conversion behavior of Co ions (Equation 3), BiCoO 3 doping of KNbO 3 can be considered acceptor-doped, as represented by the following equation:…”

Magnetic, Optical, and Impedance Spectroscopy of Barium-Substituted Lithium Ferrite

“…Figure depicts the variation of complex impedance spectra ( Z ′ vs Z ″) (Nyquist plot) at different temperatures. The expected Nyquist plot for the polycrystalline material mainly comprises two semicircular arcs due to grain and grain boundaries (relaxation time constants are different) . Information regarding the electrical process that occurs within the sample is interpreted from the behavior of the semicircle’s intercept on the real impedance axis.…”

“…The expected Nyquist plot for the polycrystalline material mainly comprises two semicircular arcs due to grain and grain boundaries (relaxation time constants are different). 65 Information regarding the electrical process that occurs within the sample is interpreted from the behavior of the semicircle's intercept on the real impedance axis. The correlation between impedance spectra and morphology is predicted by fitting an equivalent electrical circuit.…”

Significantly Enhanced Energy Storage Density of NNT Ceramics Using Aliovalent Dy3+ Dopant

“…The presence of imbricated semicircles affirms the existence of two relaxation phenomena with different relaxation times (τ = RC), where R is the resistance and C is the capacitance associated with that phase (dispersal nature of the relaxation), and most importantly, it confirms that DNNT ceramics exist in the heterogeneous form. 53,54 Generally, with increasing temperature, the intercept of the arcs on the real axis offers resistance values, which shifted toward the original plots. This phenomenon can be described as a decrease in the resistivity of DNNT ceramics due to conduction aided by the grain and the grain boundary when the temperature is increased.…”