Tuning of dielectric and ferroelectric properties in single phase BiFeO3 ceramics with controlled Fe2+/Fe3+ ratio

Single phase multiferroic BiFeO3 (BFO) ceramics were synthesized with controllable amount of Fe2+ and oxygen vacancies in a very wide concentration range. Double ferroelectric hysteresis loops are observed in fresh BFO ceramics at room temperature without any aging processes. Detailed study shows that this is due to the defect dipoles which have preferential orientations antiparallel to the direction of spontaneous polarization, providing a driving force for domain back-switching. The dielectric constant of BFO could be enormously enhanced by 100 times by increasing the Fe2+ content, employing a polaronic relaxation process.