Effects of quenching on bending strength and piezoelectric properties of (Bi_0.5Na_0.5)TiO₃ceramics

Lead-free piezoelectric bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by quenching and the correlation among a depolarization temperature Td, the mechanical strength, and their piezoelectric properties were investigated. We controlled the quenching rate in the temperature range from 1100°C to 800°C. We examined the 5 patterns of the quenching rate (QR): 0.05 (ordinary firing, OF), 3.85, 5.77, 6.67, and 15.0 (quenching) oC/s. Td of the rapid quenched sample reached 229°C (QR = 15.0), but its mechanical strength decreased to a quarter of that of the OF ceramics. On the other hand, Td was 211°C at QR = 3.85 which was higher than that of OF-ceramic (QR = 0.05) at about 180°C. Moreover, three-point bending strength (227 MPa) of the quenched BNLT4 (QR = 3.85) was equivalent to that of the OF ceramics (235 MPa). Therefore, both Td and the mechanical strength were improved by controlling the quenching rate.