Effect of BiMeO 3 on the Phase Structure, Ferroelectric Stability, and Properties of Lead‐Free Bi 0.5 (Na 0.80 K 0.20 ) 0.5 TiO 3 Ceramics

The effects of BiMeO 3 (Me = Fe, Sc, Mn, Al) addition on the phase transition and electrical properties of Bi 0.5 (Na 0.80 K 0.20 ) 0.5 TiO 3 ( BNKT 20) lead‐free piezoceramics were systematically investigated. Results showed that addition of BiFeO 3 into BNKT 20 induces a phase transition from tetragonal–rhombohedral coexisted phases to a tetragonal phase with the observation of enhanced piezoelectric properties ( d 33 = 150 pC/N for 0.02BiFeO 3 ). BiScO 3 , BiMnO 3 , and BiAlO 3 substitutions into BNKT 20 induce a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic with a significant disruption of the long‐range ferroelectric order, and correspondingly adjusts the ferroelectric–relaxor transition point T F–R to room temperature. Accordingly, large accompanying normalized strains of 0.34%–0.36% are obtained near the ferroelectric–relaxor phase boundary, and the mergence of large strain response can be ascribed to a reversible field‐induced ergodic relaxor‐to‐ferroelectric phase transformation. Moreover, our study also revealed that the composition located at the ferroelectric–relaxor phase boundary where the strain response is consistently derivable shifts to a BNKT 20‐rich composition as the tolerance factor t of the end‐member BiMeO 3 increases, and this relationship is expected to provide a guideline for designing high‐performance (Bi 0.5 Na 0.5 )TiO 3 ‐based materials by searching the ferroelectric–relaxor phase boundary.