Defect dipole-induced poling characteristics and ferroelectricity of quenched bismuth ferrite-based ceramics

Multiferroic bismuth ferrite (BiFeO₃, BFO) is one of the most promising high-temperature ferroelectric and piezoelectric materials due to a high Curie temperature (T_C ∼ 825 °C) if the enhancement of ferroelectricity and piezoelectricity can be realized. Unfortunately, it is difficult to adequately pole BFO ceramics due to a high coercive field as well as a high leakage current. Here we investigated the defect dipole-induced poling characteristics and the ferroelectric properties of four kinds of A or/and B-doped BFO ceramics (i.e. BiFeO₃, Bi_0.95Sm_0.05FeO₃, BiFe_0.95Sc_0.05O₃, and Bi_0.95Sm_0.05Fe_0.95Sc_0.05O₃) using a modified quenching technique. The piezoelectric effect is determined by the poling condition, and moreover the poling behavior is strongly dependent on the ion substitution types of BFO ceramics. An enhanced piezoelectric property (d₃₃ = 46-51 pC N^-1) can be attained without the involvement of a phase boundary. Specifically, the doping with Sm (Bi_0.95Sm_0.05FeO₃) can cause an obvious threshold during poling, and additionally Bi_0.95Sm_0.05FeO₃ and Bi_0.95Sm_0.05Fe_0.95Sc_0.05O₃ components can be curiously adequately poled below the coercive field at the poling temperature of 100 °C. In addition, the saturated P-E loops with an obvious internal bias field (E_i) were observed, where E_i was induced by defect dipoles, and then defect dipoles may be decoupled at 120 °C and 6 kV mm^-1 (DC field), resulting in a cyclical poling current. It is of great interest to note that an enhanced remanent polarization (2P_r ∼ 50-60 μC cm^-2) of the ceramics is obtained, and especially the internal bias fields can be alleviated by AC-cycling or decreasing the measurement frequency. Finally, we believe that our research will have a significant importance in the improvement of piezoelectricity of BFO-based ceramics.