Phase Transitional Behavior and Piezoelectric Properties of Lead‐Free (Na 0.5 K 0.5 )NbO 3 –(Bi 0.5 K 0.5 )TiO 3 Ceramics

(1− x )(Na 0.5 K 0.5 )NbO 3 –(Bi 0.5 K 0.5 )TiO 3 solid solution ceramics were successfully fabricated, exhibiting a continuous phase transition with changing x at room temperature from orthorhombic, to tetragonal, to cubic, and finally to tetragonal symmetries. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was found at 2–3 mol% (Bi 0.5 K 0.5 )TiO 3 (BKT), which brings about enhanced piezoelectric and electromechanical properties of piezoelectric constant d 33 =192 pC/N and planar electromechanical coupling coefficient k p =45%. The MPB composition has a Curie temperature of 370°–380°C, comparable with that of the widely used PZT materials. These results demonstrate that this system is a promising lead‐free piezoelectric candidate material.