Unidirectional Electrobending Deformation in Acceptor-Doped Piezoceramics

Since 2022, large apparent strains (>1%) with highly asymmetrical strain-electric field (S-E) curves have been reported in various thin piezoceramic materials, attributed to a bidirectional electric-field-induced bending (electrobending) deformation, which consistently produces convex bending along the negative electric field direction. In this study, a novel unidirectional electrobending behavior in acceptor-doped K_0.5Na_0.5NbO₃ ceramics are reported, where convex bending always occurs along the pre-poling direction regardless of the direction of the applied electric field. This unique deformation is related to the reorientation of the ( $M_{\mathrm{Nb}}^{{}^{\text{'}\text{'}\text{'}}}-V_O^{··}$ ) defect dipoles (where M²⁺ represents the acceptor-doped ion in the Nb- site) in one surface layer during the pre-poling process, resulting in an asymmetrical distribution of defect dipoles in the two surface layers. The synergistic interaction between ferroelectric domains and defect dipoles in the surface layers induces this unidirectional electrobending, as evidenced by a butterfly-like symmetrical bipolar S-E curve with a giant apparent strain of 3.2%. These findings provide new insights into defect engineering strategies for developing advanced piezoelectric materials with large electroinduced displacements.