Synthesis and Characterization of Potassium-Sodium Niobate K0.5Na0.5NbO3 Obtained by the Microwave Method

A hydrothermal–microwave method was developed for the synthesis of potassium–sodium niobate K0.5Na0.5NbO3 (KNN) followed by high-temperature microwave treatment to obtain KNN ceramics. The synthesis was carried out in a microwave reactor at 210°C for 60 min. A KNN powder was obtained, consisting predominantly of agglomerates formed by nanocrystalline particles (crystallites) with sizes of 20–25 nm. X-ray diffraction analysis confirmed the formation of a single-phase orthorhombic perovskite structure of potassium–sodium niobate at relatively low temperatures (200–220°C). After heat treatment in the temperature range of 660–1100°C, the crystallite size increased up to 90 nm, accompanied by grain growth to the micrometer scale, indicating sintering with the formation of KNN ceramics. Measurements revealed a strong temperature dependence of the dielectric properties of KNN samples. Based on the obtained dielectric parameters, the piezoelectric coefficients were estimated, and according to this theoretical evaluation, the material is capable of exhibiting a significant piezoelectric effect. The maximum piezoelectric coefficient d33 of approximately 160–180 pC/N was observed for samples sintered at 660°C. It was established that precise control of the heat-treatment temperature is crucial for optimizing the structure–property relationship in lead-free KNN-based piezoceramics.