Piezoelectric properties of lead-free ferroelectric ceramics under some specifc conditions

Throughout our research about lead-free piezoelectric ceramics, we have found that some of lead-free ferroelectric ceramics indicate the excellent piezoelectric properties as compared with PZT-based ceramics under some specific conditions such as high temperature, large amplitude vibration or large mechanical stress. Bismuth layer-structured ferroelectric ceramic, Bi₄Ti₃O₁₂ (BIT), has high Curie temperature, T_c, at about 680°C. And the grain oriented BIT ceramics with V doping show large piezoelectric voltage constant, g33, of approximately 30×10-3 Vm/N, which are possible candidate performance for sensors and other piezoelectric devices at high temperature. In the case of high-power piezoelectric properties, (Bi_0.5Na_0.5)TiO₃ (BNT)-based solid solutions and BLSF ceramics maintain large mechanical quality factor Q_m even in the large amplitude vibration. (Normally, the Q_m of PZT-based ceramics drops down under the large amplitude vibration above 1 m/s) That is very good advantage for achieving the large vibration velocities more than 2 m/s. Additionally, Bi-based lead-free ceramics indicated high mechanical strength as compared with PZT-based ceramics. From these results, some of lead-free ceramics are possible candidates to be used for specific piezoelectric devices under high temperature, large vibration velocities or large mechanical stress.