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

Abstract

High-performance (Na_0.5Bi_0.5)TiO₃ (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 (d₃₃*) of 810 pm V⁻¹ at a low driving field of 4 kV mm⁻¹ in a novel ternary (0.94 − x)(Na_0.5Bi_0.5)TiO₃–0.06Ba(Zr_0.05Ti_0.95)O₃−x(Sr_0.8Bi_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.