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

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 epsilon(r) values of grains for SrTiO3 and Ca0.9Sr0.1TiO3 ceramics are 193.8 and 138.1, respectively, confirming that dielectric response of the high-epsilon(r) 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 epsilon(r) similar to 148 of grains than epsilon(r) similar to 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 epsilon(g) similar to 17.8 and epsilon(gb) similar to 20.8, and the combination of them is close to epsilon(r) similar to 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.