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 (Pd) oriented along or close to the poling direction. Pd 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.