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.
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(Ba0.2Sr0.2Ca0.2Bi0.2Na0.2)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 d*33 ∼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.
The development of ferroelectric ceramics with both large piezoelectric responses and broad service temperature range is still a key challenge for practical applications due to the so-called d 33 - T C trade-off. Here we report the strategy to utilize the synergistic contribution of morphotropic phase boundary and enhanced local structural heterogeneity, in which an excellent piezoelectric coefficient d 33 of 680 pC/N and a high Curie temperature of 330 ℃ are simultaneously achieved in Sm modified 0.25PIN-0.325PZ-0.425PT ceramics. The underlying mechanism responsible for the high dielectric and piezoelectric properties is studied based on cryogenic dielectric measurement and Rayleigh analysis. Of particular interest is that, a high field-induced strain of 0.19% is achieved in 0.25PIN-0.32PZ-0.43PT at electric field of 20 kV/cm, corresponding to a piezoelectric d 33 * of 945 pm/V, showing an excellent temperature stability with minimal variation of 7% up to 310 °C. This work demonstrates the introduction of high temperature end members and rare earth doping are conducive to ferroelectric solid solutions with desired broad usage temperature range and superior piezoelectric properties , which will greatly benefit high temperature actuator applications.
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