Cycling stability of lead-free BNT-8BT and BNT-6BT-3KNN multilayer actuators and bulk ceramics

This study presents the electromechanical properties and cycling stability of lead-free piezoelectric materials 0.92(Bi1/2Na1/2)TiO3-0.08BaTiO3 (BNT-8BT) and 0.91(Bi1/2Na1/2)TiO3-0.06BaTiO3-0.03(K0.5Na0.5)NbO3 (BNT-6BT-3KNN). Both bulk samples as well as multilayer actuators (MLA) with internal Ag/Pd (70/30) electrodes were successfully processed from both materials. Electromechanical characteristics in the non-fatigued state and after different numbers of unipolar fatigue cycles are provided, representing the first direct comparison of the fatigue resistance of lead-free bulk ceramics and the corresponding MLAs. At a maximum field of 6 kV/mm and a frequency of 50 Hz, BNT-8BT MLA delivered a maximum strain of 0.07% and displayed excellent cycling stability. BNT-6BT-3KNN MLA provided a higher strain of 0.15% initially but degraded during cycling and exhibited break down after 107 cycles. Furthermore, the frequency dependence of strain and the self-heating during cycling were investigated. The temperature increase is limited only to 2 °C in BNT-8BT MLA and 13 °C in BNT-6BT-3KNN MLA.