Enhanced extrinsic domain switching strain in core-shell structured BaTiO<inf>3</inf>-KNbO<inf>3</inf> ceramics

Abstract Large electric-field-induced strain in piezoelectric ceramics is a primary requirement for their actuator applications. This macroscopic strain is generated from both intrinsic lattice strain and extrinsic domain switching and/or phase transformations. Among these contributions, non-180°ferroelectric domain switching can generate a large electric-field-induced strain due to the change in orientation of the coupled spontaneous strain. However, the large fraction of non-180°ferroelectric domain switching is a one-time effect during electrical poling. Here, we show that electric-field-induced non-180°ferroelectric domain switching in the microstructurally engineered material BaTiO3-KNbO3 (BT-KN) is largely reversible. In situ high energy X-ray diffraction showed approximately 95% reversibility in the switched fraction of non-180°ferroelectric domains during unipolar cycling. This reversibility is hypothesised to be due to the unique grain boundary structure of this material, where ferroelectric domain walls do not interact strongly with grain boundary defects. The domain switching behaviour of core-shell BT-KN has been contrasted with that of polycrystalline BaTiO3 and commercial lead zirconate titanate Pb(Zr,Ti)O3. The large and reversible non-180°ferroelectric domain switching of core-shell BT-KN offers a distinctive strain response. The results indicate a unique family of large strain lead-free materials based on enhanced reversible non-180°ferroelectric domain switching can be developed for future actuator applications