Enhancing Electrical Properties in NBT–KBT Lead‐Free Piezoelectric Ceramics by Optimizing Sintering Temperature

Conventional sintering of (Na 1− x K x ) 0.5 Bi 0.5 TiO 3 (abbreviated as NKBT x , x =18–22 mol%) lead‐free piezoelectric ceramics was investigated to clarify the optimal sintering temperature for densification and electrical properties. Both sintered density and electrical properties were sensitive to sintering temperature; particularly, the piezoelectric properties deteriorated when the ceramics were sintered above the optimum temperature. The NKBT20 and NKBT22 ceramics synthesized at 1110°–1170°C showed a phase transition from tetragonal to rhombohedral symmetry, which was similar to the morphotropic phase boundary (MPB). Because of such MPB‐like behavior, the highest piezoelectric constant ( d 33 ) of about 192 pC/N with a high electromechanical coupling factor ( k p ) of about 32% were obtained in the NKBT22 ceramics sintered at 1150°C.