Utilization of Nonstoichiometric Nb⁵⁺ to Optimize Comprehensive Electrical Properties of KNN-Based Ceramics

An easy approach is suggested to obtain excellent piezoelectric performances in potassium sodium niobate (KNN)-based ceramics simultaneously with low dielectric loss (tanδ), high Curie temperature (T_C), and electromechanical coupling factor (k_p). Herein, a KNN-based ceramics system with nonstoichiometric Nb⁵⁺ is designed. Excessive Nb⁵⁺ occupying the B-site significantly influences the microstructural features and electrical properties of KNN-based ceramics. Furthermore, the excessive Nb⁵⁺ improves the temperature stability of ceramics by providing the domain wall pegging effect and defect dipole. A high T_C = 300 °C, large k_p = 0.516, and d₃₃ = 450 pC/N can be simultaneously obtained in the KNN-based ceramics with nonstoichiometric Nb⁵⁺. These results confirm that the comprehensive electrical properties of KNN-based ceramics can be tuned by optimizing the content of nonstoichiometric Nb⁵⁺.