Giant electro-induced strain in lead-free relaxor ferroelectrics via defect engineering

Lead-free relaxor ferroelectric (RFE) ceramics find application in a broad range of technological devices due to their large electrostrain. But few lead-free ceramics show electrostrain values of more than 1 %. Here, an extraordinary strategy to obtain giant electrostrain by manipulating defect dipoles in (Bi, Na)TiO₃-BaTiO₃-based RFE ceramics is developed, achieving a high electro-induced strain value of 1.68 %, with a corresponding effective piezoelectric coefficient (d*₃₃) of 1965 pm/V. Furthermore, the effect of defect dipoles on RFE ceramics is discussed. The defects are pinned after poling, forming defect dipoles polarization (P_d) oriented along or close to the poling direction. P_d significantly promotes the transformation of polar nano regions to ferroelectric domains during strain-electric field (S-E) cycles, resulting in ultra-high electrostrain. This work proposes a detailed mechanism considering defect dipoles coupling in RFE ceramics and provides a promising paradigm for achieving high electrostrain, which could be applied in designing a wide range of functional ceramics.