Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO 3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O 3 ’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na 0.56 K 0.44 )NbO 3 −0.03Bi 0.5 Na 0.5 ZrO 3 −0.03(Bi 0.5 K 0.5 )HfO 3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d 33 of 550 ± 30 pC/N and ultrahigh temperature stability ( d 33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d 33 change rate of the commercial Pb(Zr, Ti)O 3 −5 ceramics is only about 10%, and more importantly, its d 33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO 3 -based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO 3 -based ceramics.