Thermal Quenching Effects on the Ferroelectric and Piezoelectric Properties of BiFeO3-BaTiO3 Ceramics

By modification of the heat-treatment process to avoid the intermediate temperature range where secondary phases are easily formed in BiFeO3, piezoelectric properties were improved; the direct piezoelectric sensor coefficient d 33 increased from 240 to 352 pC/N in 0.67BiFeO(3)-0.33BaTiO(3) (BF33BT) ceramic and from 402 to 454 pC/N in 1 mol % BiGaO3-doped BF33BT (BG) ceramic with almost unchanged high Curie temperatures around 454 degrees C. To understand the effects of water quenching after sintering, eight different BF33BT ceramics were prepared by using different cooling routes together with furnace-cooled and water-quenched BG ceramic. Structural, ferroelectric, and piezoelectric properties of these ceramics were compared. All after-annealed BF33BT ceramics were compared with quenched ceramics. Physical properties of the after-annealed ceramics were similar to those of the furnace-cooled ceramic. It was confirmed that the overall duration of heat treatment in the second-phase-forming intermediate temperature range plays an important role in processing BF33BT ceramics without secondary phases or defects.