Electrical properties and thermally stable property of lead-free BNT-BT-KNN ceramics at the morphotropic phase boundary region

Lead-free BNT-BT based ceramics exhibit significant potential for achieving high piezoelectric performance. However, it is an effective strategy to achieve a morphotropic phase boundary (MPB) region with good thermal stability remains challenging. Herein, the incorporation of K 0.5 Na 0.5 NbO 3 into the Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 binary system was explored, leading to a significant enhancement in both piezoelectric performance and thermal stability. The ternary BNT-BT-KNN ceramic system was systematically investigated with respect to its phase diagram, crystal structure, electrical properties, and relaxation behavior. It was observed that both the grain size and domain size gradually decrease as the KNN content increases. Remarkable electromechanical coupling factor ( k p  = 0.217), exceptionally high piezoelectric properties ( d 33  = 105 pC/N), and improved ( T d  = 164 °C) were achieved at BNT-BT-0.01KNN ceramics. The phase diagram of BNT-BT-KNN has been established, offering a comprehensive roadmap for the development of high-performance piezoelectric ceramics with enhanced piezoelectric responses. This work may facilitate potential applications in piezoelectric actuators.