Piezoelectric and dielectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5K_0.5TiO₃–Ba_0.77Ca_0.23TiO₃ lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5(Na_0.84K_0.16)_0.5TiO₃–xBa_0.77Ca_0.23TiO₃ (BNKT–xBCT, x = 0–0.04) were synthesized by conventional solid-state reaction method. The piezoelectric, dielectric, and ferroelectric characteristics of the ceramics are investigated and discussed. The XRD results show that Ba_0.77Ca_0.23TiO₃ (BCT) has diffused into Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ (BNKT) lattices to form a new solid solution. It is shown that moderate additive of BCT (x ≤ 0.025) in BNKT–xBCT ceramics can enhance their piezoelectric and ferroelectric properties. Three dielectric anomalies are observed in BNKT–xBCT (x ≤ 0.03) ceramics. The piezoelectric measurements and P–E hysteresis loops reveal that BNKT–0.025BCT ceramic has the highest piezoelectric performance and strongest ferroelectricity in all the samples. Piezoelectric constants d ₃₃, k _p, and k _t of 175 pC/N, 29.1, and 54% are, respectively, achieved. Remnant polarization P _r and coercive field E _c reach 28.3 μC/cm² and 24.2 kV/cm, respectively.