Dielectric properties and impedance analysis of BaTiO3-based ceramics with core-shell structure

In this paper, a core-shell structure, where the BaTiO3 (BT) particles were coated with 0.25Bi(Zn1/2Ti1/2)O3-0.75BaTiO3 [BT@x(0.25BZT-0.75BT)] by sol-gel method, was fabricated and confirmed by transmission electron microscopy (TEM). The impedance data of BT, 0.25BZT-0.75BT and BT@x(0.25BZT-0.75BT) (x=0.5-1.0) ceramics was collected and fitted by different equivalent circuits. The core and shell regions of BT@x(0.25BZT-0.75BT) (x=0.5-1.0) ceramics can be separated in complex impedance plots (fitted by a 4RC equivalent circuit), according to the activation energies of BT and 0.25BZT-0.75BT. The calculated activation energy of the core part in BT@x(0.25BZT-0.75BT) ceramics is relatively stable, being closer to the activation energy (0.86 eV) of BT, while the activation energy of the shell was found to increase from 0.28 eV to 0.53 eV with increasing the shell thickness. The average core/shell ratio (dgc/dgs) for BT@0.8(0.25BZT-0.75BT) ceramics was found to be on the order of 7.26, calculated by a modified two-layer dielectric model. In addition, Lichtenecker formula was used to simulate the dielectric constant of BT@0.8(0.25BZT-0.75BT) ceramics at room temperature and the simulated results are in agreement with the measured values.