Bipolar and unipolar fatigue property in Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 lead-free piezoelectric ceramics

The bipolar and unipolar fatigue property of lead-free piezoelectric solid solution Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 (BNKST) was studied. Under a bipolar electric field of 4 kV/mm at 10 Hz, the remnant and maximum polarization, maximum strain value of all the studied compositions changed less than 2% after 10(6) bipolar cycles, while the coercive field exhibited different behavior for BNKST composition with different ferroelectric order states. The unipolar fatigue results also indicated that the BNKST with SrTiO3 concentration of 0.15 had excellent fatigue property after 10(7) unipolar cycles under 4 kV/mm. The underlying mechanism was discussed. The excellent fatigue property and large strain response make this system suitable for piezoelectric actuator applications.