Realization of densified microstructure and large piezoelectricity in KNN ceramics via the addition of oxide additives

摘要

Lead-free potassium sodium niobate [(K, Na)NbO_3, KNN]-based ceramics have aroused great interest due to their excellent piezoelectricity and high Curie temperature. However, the deteriorative microstructure of KNN-based ceramics restricts their further developments. In this work, various kinds of oxide additives (Al_2O_3 ,Co_2O_3, Nb_2O_5, SnO_2 and HfO_2) are introduced into the KNN-based ceramics to increase the grain size and wipe the microcracks to improve their microstructures. Herein, large piezoelectric coefficient values (d_(33) ≈ 450-500 pC/N) and high Curie temperature values (T_C ≈ 255-263 °C) together with high electromechanical coupling coefficient values (k_p≈ 0.50-0.56) are obtained in constructed R-O-T multiphase coexisted KNN-based ceramics. Moreover, the KNN ceramic with the addition of Al_2O_3 exhibits an optimal unipolar strain value (S = 0.124%) and a high inverse piezoelectric constant (d_(33)* = 494 pm/V). We believe that our findings provide a simple, effective, and applicable approach to optimize the electrical performances of KNN-based system materials.