Nonstoichiometric Effects in the Leakage Current and Electrical Properties of Bismuth Ferrite Ceramics

To understand the defect chemistry of multiferroic BiFeO3-based systems, we synthesized nonstoichiometric Bi1+xFeO3 +/-delta ceramics by conventional solid-state reaction method and studied their structural, dielectric and high-temperature charge transport properties. Incorporation of an excess amount of Bi2O3 lowered the Bi deficiency in BiFeO3. Polarization versus electric field (P-E) hysteresis loop and dielectric properties were found to be improved by the Bi2O3 addition. To better understand the defect effects on the multiferroic properties, the high temperature equilibrium electrical conductivity was measured under various oxygen partial pressures (pO(2)'s). The charge transport behavior was also examined through thermopower measurement. It was found that the oxygen vacancies contribute to high ionic conduction, showing pO(2) independency, and the electronic carrier is electron (n-type) in air and Ar gas atmospheres.