THE AC ELECTRICAL BEHAVIOR OF HYDROTHERMALLY SYNTHESIZED BARIUM-TITANATE CERAMICS

The ac electrical response of hydrothermally synthesized polycrystalli ne barium titanate (BaTiO3) was studied as a function of frequency usi ng immittance measurements at temperatures ranging from 200 to 500 deg rees C in air. Two semicircular relaxations were observed in impedance (Z) and modulus (M*) planes. The capacitance of the high-frequency r elaxation obtained from these complex planes showed a Curie-Weiss beha vior originating from a lumped grain contribution. The low-frequency r elaxation exhibited a high capacitance which was invariant with temper ature, suggesting a possible grain-boundary contribution. The grain-bo undary resistance was found to be higher than that of grains at all te mperatures. An equivalent circuit consisting of two parallel RC combin ation in series is evident from the Z- and M*-plane analyses, and rep resents the individual contribution of grain and grain-boundary region s of the polycrystalline sample. Another circuit consisting of a serie s RC combination in parallel with a de resistance (R(0)) and a high-fr equency limit capacitance (C-infinity) is identified. This circuit por trays a possible trapping effect revealed by the admittance (Y) and c apacitance (C) plane analyses. The two circuits are equivalent and co mplementary to each other as they together provide more information on the operative electrical processes in the sample.