Dielectric relaxation and conductivity phenomena in ferroelectric ceramics at high temperatures

The issues related to microstructure and its effects on functional properties of electroceramics become increasingly prominent with the progressive downscaling of electronics. In this study, temperature-dependent dielectric and impedance data of BaTiO3 (BT), Sr-doped BT (BST) and layer-structured BaBi4Ti4O15 (BBTO) ceramics are systematically investigated to reveal the effects of doping and perovskite layering on the dielectric relaxation and conduction processes at high temperatures. By using complex impedance spectroscopy, it is demonstrated that the ceramics are electrically heterogeneous structures displaying a non-ideal Debye-like behavior at high temperatures. Using a suitable equivalent circuit model, the impedance diagrams at different temperatures are simulated and the refined values of macroscopic resistance and capacitance are used for the identification and characterization of particular microstructural regions (grains, grain boundaries, interfaces, etc.). The approach of combining the impedance, electric modulus and permittivity formalisms is demonstrated to be effective in explaining the peculiarities of the electrical charge transport mechanism and relaxation in the grains, grain boundaries and interface layers of the ceramics.