Giant electrostrain accompanying structural evolution in lead-free NBT-based piezoceramics

High-performance (Na 0.5 Bi 0.5 )TiO 3 (NBT) lead-free incipient ceramics are promising piezoactuator materials, but high driving fields to deliver the large strain limits their practical applications. Herein, we report a giant piezoelectric strain ( d 33 *) of 810 pm V −1 at a low driving field of 4 kV mm −1 in a novel ternary (0.94 − x )(Na 0.5 Bi 0.5 )TiO 3 -0.06Ba(Zr 0.05 Ti 0.95 )O 3 − x (Sr 0.8 Bi 0.1 0.1 )TiO 2.95 solid solution with x = 0.05 (SBT5). The field of SBT5 critical composition is notably reduced compared with other NBT-based ceramics, while its strain properties are maintained at a high level along with an excellent thermal stability. The dopant induces a randomly distributed local polarization field, which breaks the symmetry of Landau potential curves, boosts the ferroelectric instability and favors a more disordered relaxor structure. The giant strain in the critical composition SBT5 is due to a field-induced reversible relaxor-ferroelectric phase transformation, while the reduced driving field results from two synergistic effects: remanent quasi-ferroelectric order as the seed for the growth of polar domains helps the system skip the nucleation process; the local defects further facilitate the growth of ferroelectric domains. The composition, temperature and electric-field dependence of structural evolutions were systematically elucidated from the micro- and macroscopic view. This study opens up a feasible and effective way for achieving giant electrostrain in lead-free actuator materials. Lead-free NBT-based piezoceramics: local defects boost ferroelectric instability and giant electrostrain.