Insight into the evolutions of microstructure and performance in bismuth ferrite modified potassium sodium niobate lead-free ceramics

In consideration of growing human health and ecological environment issues, lead-free piezoelectric ceramics have aroused heated research to develop their potential applications in electronic fields instead of toxic lead-based ones. In the present work, a ternary lead-free material system of (0.97-x)K0.48Na0.52Nb0.96Sb0.04O3–0.03Bi0.5Na0.5Zr0.8Sn0.2O3-xBiFeO3 (KNNS-BNZS-xBF, 0 ≤ x ≤ 0.007) ceramics was designed, and the evolution mechanisms of microstructures and electrical behaviors at multiple applied fields were revealed in detail. The bimodal microstructure with an alternative fine and coarse grain size distribution feature is generally observed, while the BF doping tends to decrease grain size and increase the diffusion phase transition behaviors. As x = 0.005, the R-O-T multiphase boundary is formed at room temperature, accompanied by the presence of striped nanodomains with smaller size and regular distribution feature that exhibit the better polarization switching and the fast domain wall movement under external stimuli. In particular, an enhanced d33 ∼ 470 pC/N and a simultaneous higher Tc ∼ 260 °C are achieved in KNNS-BNZS-0.005BF, reflecting a better balanced development of performance by the present doping strategy. Most importantly, benefiting from the coexistence of R-O-T multiphase boundary and the lower domain wall energy, an excellent d33⁎ ∼ 530 pm/V is attained as well in this ceramic, which favors the better applications in high precision displacement or strain actuators. This work sheds insight into understanding the underlying physical mechanism of enhanced performance of KNN-based ceramics, substantially expanding the more applications of lead-free piezoelectric materials in electronic fields. •A new lead-free material system of KNNS-BNZS-xBF is designed.•Enhanced comprehensive performance is obtained by constructing R-O-T multiphase boundary.•The domain structures and polarization switching behaviors are revealed in detail.•The physical origin of enhanced performance is elaborated.