Dielectric and Ferroelectric Properties of KNN Ceramics Fabricated by Microwave Sintering

(K,Na)NbO₃(KNN)-based ceramics are a promising lead-free piezoelectric material that could replace Pb(Zr_1−xTi_x)O₃-based materials due to their higher Curie temperature and superior electrical properties. However, the volatilization of sodium and potassium during conventional high-temperature sintering makes it difficult to obtain KNN ceramics with a dense structure and excellent electrical properties. Herein, a conventional solid-phase method combined with microwave sintering is applied for the preparation of KNN ceramics. The influence of the microwave sintering process on the microstructure and electrical properties of KNN ceramics were studied. The optimal microwave sintering conditions for KNN ceramics were determined to be 1100°C for 50 min. Under these conditions, the ceramic samples exhibited excellent ferroelectric properties, with the maximum polarization (P_max) of 20.4 μC/cm² and a remanent polarization (P_r) of 18.1 μC/cm². Additionally, the samples demonstrated impressive piezoelectric properties, including the maximum electric field-induced strain (S_max) of 0.0251%, a dynamic piezoelectric coefficient (d₃₃*) of 125.5 pm/V, and a piezoelectric coefficient (d₃₃) of 109.8 pC/N. The study has important implications for the use of microwave sintering to achieve the densification of the ceramic with volatile elements such as KNN-based ceramics at lower sintering temperature and short sintering time.