Internal stress optimization enhancing the properties of KNN-based Ni-internal-electrode multilayer piezoelectric actuators

The KNN-based Ni-internal-electrode multilayer piezoelectric actuators (MLAs) possess the advantages of environmental friendliness and low cost. However, the internal stresses in MLAs suppress the performance of ceramic materials and should be optimized for improving the comprehensive performances of MLAs. This study alleviated the generation of internal stresses in MLAs by modifying the electrode pastes and designing the shapes of the internal electrodes, increasing the inverse piezoelectric coefficient d 33 * to 450 pm/V. The temperature stability of MLAs is significantly improved compared to the bulk ceramics, indicating that the internal stresses can also play a positive role in MLAs. In addition, the MLAs experience only a 4.7 % decrease in d 33 * over 5 million fatigue cycles due to the possible delayed propagation of fatigue cracks. The improvement of material properties and the solution to application problems should complement each other, jointly promoting the practicality of lead-free piezoceramics.