Defect dipole induced large recoverable strain and high energy-storage density in lead-free Na0.5Bi0.5TiO3-based systems

Ferroelectric crystals are characterized by their asymmetric or polar structures. In an electric field, ions undergo asymmetric displacement and result in a small change in crystal dimension, which is proportional to the applied field. Such electric-field-induced strain (or piezoelectricity) has found extensive applications in actuators and sensors. However, the effect is generally very small and thus limits its usefulness. Here I show that with a different mechanism, an aged BaTiO(3) single crystal can generate a large recoverable nonlinear strain of 0.75% at a low field of 200 V mm(-1). At the same field this value is about 40 times higher than piezoelectric Pb(Zr, Ti)O(3) (PZT) ceramics and more than 10 times higher than the high-strain Pb(Zn(1/3)Nb(2/3))O(3)-PbTiO(3) (PZN-PT) single crystals. This large electro-strain stems from an unusual reversible domain switching (most importantly the switching of non-180 degrees domains) in which the restoring force is provided by a general symmetry-conforming property of point defects. This mechanism provides a general method to achieve large electro-strain effect in a wide range of ferroelectric systems and the effect may lead to novel applications in ultra-large stroke and nonlinear actuators.