Giant electro-strain nearly 1% in BiFeO3-based lead-free piezoelectric ceramics through coupling morphotropic phase boundary with defect engineering

Abstract

Ultrahigh strain and large piezoelectric coefficient in ferroelectric ceramics are always desired for actuator application. However, a long-standing challenge is the reported electro-strain value in lead-free ceramics encountering a bottleneck of 0.8%. Meanwhile, ultrahigh strain requires sufficiently high electric field, thus leading to the incompatibility of large strain with a low large-signal piezoelectric coefficient d33∗. In this work, we report a novel material design strategy that coupling morphotropic phase boundary and defect engineering realize a giant recoverable electro-strain nearly 1.0% and a large-signal piezoelectric coefficient d33∗ = 1212.5 pm/V in 0.695BiFeO3–0.3BaTiO3–0.005Bi(Zn0.5Ti0.5)O3 ceramic, which is the largest strain value so far in reported lead-free ceramics. Structural investigations reveal that this electro-strain is tightly associated with the abundant polar nanoregions (PNRs) in phase boundary and internal bias field induced by defect dipoles via eliminating negative strain combining with asymmetric strain behavior. The coexistent phases and their PNRs with increasing structural flexibility as well as internal bias field aiding polarization orientation are responsible for the extremely high piezoelectric response. This work will afford a paradigm to optimize the strain properties and stimulate new development of lead-free oxides for actuators applications.