Giant Electrostrain in Lead-Free Textured Piezoceramics by Defect Dipole Design

By converting electrical signal into mechanical displacement, piezoelectric actuators are widely used in many applications due to their precise displacement, fast response, and small size. The unipolar electrostrain values larger than 1% reported so far are from lead-based single crystals or ceramics, which brings environmental concerns. Herein, a giant unipolar electrostrain of 1.6% with good fatigue resistance and low hysteresis in Sr/Nb-doped Bi_0.5 (Na_0.82 K_0.18 )_0.5 TiO₃ lead-free textured piezoceramics by defect dipole design is reported, which is comparable to or even higher than state-of-the-art lead-based piezoelectric single crystals. The engineered defect dipoles in ergodic relaxor ferroelectrics can introduce a large internal bias field along the poling direction, where the 〈111〉-oriented defect dipoles with large polarizability aligning along the 〈111〉-oriented spontaneous polarizations of the electric-field-induced ferroelectric phase greatly benefit the reversible phase-transition process of the 〈00l〉-textured ceramic. In-depth microstructural studies reveal that the greatly enhanced electrostrain is realized by the synergistic contributions from the reversible electric-field-induced phase transition, grain orientation engineering, and most importantly, defect dipole engineering. The present research provides a general strategy for the design of piezoceramics with high electrostrain, which is expected to be promising alternative to lead-based piezoelectric actuators.