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

Abstract The AC impedance of SrTiO 3 , Ca 0.9 Sr 0.1 TiO 3 , Ca 0.7 Sm 0.2 TiO 3 , and Ca 0.7 Sm 0.3 Ti 0.7 Al 0.3 O 3 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 ε r values of grains for SrTiO 3 and Ca 0.9 Sr 0.1 TiO 3 ceramics are 193.8 and 138.1, respectively, confirming that dielectric response of the high‐ ε r microwave ceramics is contributed to the grains, at microwave frequencies. Impedance spectroscopy of Ca 0.7 Sm 0.2 TiO 3 ceramic illustrates that electrical heterogeneous microstructures include interior grains and grain shells. The secondary phase existing in Ca 0.7 Sm 0.2 TiO 3 ceramic causes deviation in bulk permittivity, resulting in a higher ε r ~ 148 of grains than ε r ~ 112 of bulk permittivity, measured at microwave frequencies. Grain and grain‐boundary impedance of Ca 0.7 Sm 0.3 Ti 0.7 Al 0.3 O 3 ceramic cannot be separated completely. The permittivities of grains and grain boundaries in Ca 0.7 Sm 0.3 Ti 0.7 Al 0.3 O 3 ceramic are ε g ~ 17.8 and ε gb ~ 20.8, and the combination of them is close to ε r ~ 40 at microwave frequencies. The Log I −Log U curves of the ceramic system indicate that the conducting mechanism of grains and grain boundaries follows ohmic behavior.