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 Bi0.5 (Na0.82 K0.18 )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.
Keywords: defect dipoles; electrostrain; lead-free piezoceramics; texture.
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