Bismuth Ferrite-Based Lead-Free High-Entropy Piezoelectric Ceramics

Piezoelectric ceramics, as essential components of actuators and transducers, have captured significant attention in both industrial and scientific research. The "entropy engineering" approach has been demonstrated to achieve excellent performance in lead-based materials. In this study, the "entropy engineering" approach was employed to introduce the morphotropic phase boundary (MPB) into the bismuth ferrite (BF)-based lead-free system. By employing this strategy, a serial of novel "medium to high entropy" lead-free piezoelectric ceramics were successfully synthesized, namely (1-x)BiFeO₃-x(Ba_0.2Sr_0.2Ca_0.2Bi_0.2Na_0.2)TiO₃ (BF-xBSCBNT, x = 0.15-0.5). Our investigation systematically examined the phase structure, domain configuration, and ferroelectric/piezoelectric properties as a function of conformational entropy. Remarkable performances with a largest strain of 0.50% at 100 kV/cm, remanent polarization ∼40.07 μC/cm², coercive field ∼74.72 kV/cm, piezoelectric coefficient ∼80 pC/N, and $$ ∼500 pm/V were achieved in BF-0.4BSCBNT ceramics. This exceptional performance can be attributed to the presence of MPB, coexisting rhombohedral and cubic phases, along with localized nanodomains. The concept of high-entropy lead-free piezoelectric ceramics in this study provides a promising strategy for the exploration and development of the next generation of lead-free piezoelectric materials.