Ferroelectric and piezoelectric properties of (Na, K)0.5Bi0.5TiO3lead free ceramics

(1 − x )Na 0.5 Bi 0.5 TiO 3 − x K 0.5 Bi 0.5 TiO 3 (NKBT100 x ; x being the mole ratio) piezoelectric ceramics were prepared by a conventional solid reaction method. The microstructure and ferroelectric properties of NKBT100 x solid solution ceramics with compositions of Na 0.5 Bi 0.5 TiO 3 (NBT)-rich and K 0.5 Bi 0.5 TiO 3 (KBT)-rich were investigated by SEM, XRD, temperature dependence of dielectric constant, and hysteresis loop, respectively. XRD studies showed that the pure perovskite structure existed in NKBT100 x ceramics with x ⩽ 0.50, while a small amount of a second phase, K 4 Ti 3 O 8 , appeared in the ceramics with x ⩾ 0.70 due to the structural instability of KBT-rich ceramics. The grain size decreased with increasing KBT content, showing that the KBT-rich solid solutions were very difficult to densify fully. The temperature dependence of the dielectric constant of NKBT100 x ceramics showed that the depolarization temperature ( T d ) reached a minimum value at the composition of x = 0.16 (NKBT16) near the morphotropic phase boundary, which suggested that the ferroelectric state of co-existence between the rhombohedral phase of NBT and tetragonal phase of KBT were not as stable as the single phase of NBT and KBT, respectively. The poled density NKBT50 ( x = 0.50) showed high piezoelectric properties, high T d and low dielectric loss, which was a good candidate for lead free piezoelectric ceramics working at relatively high temperatures.