Balanced development of dielectric permittivity, loss tangent, and temperature stability in K_0.5Na_0.5NbO₃-based ceramic capacitors

Ceramic capacitors are extremely expected to attain the high dielectric permittivity (ε′) and low loss tangent (tanδ) stabilized in an ultra-wide operating temperature range. In this work, we improved ε′, tanδ and their temperature stability by tailoring the distortion of oxygen octahedron with a different chemical composition in the K_0.5Na_0.5NbO₃-based materials, and the relationships among the composition, crystal structure and dielectric performances were systematically investigated. By designing a series of material systems of K_0.5Na_0.5NbO₃-0.02BiMO₃ {KNN-M, M: Al, Fe, (Ti_0.5Mg_0.5), (Ti_0.5Zn_0.5), (Nb_1/3Zn_2/3)}, the decreased distortion of oxygen octahedron and enhanced symmetry in crystal structure could be well established, and a high dielectric permittivity (ε’ = 1130 ± 15%) with stability in 25 °C–500 °C range was achieved in the KNN-NbZn ceramics. Particularly, a low loss tangent (tanδ ≤ 3%) was maintained up to 360 °C in the ceramics. Therefore, a balanced development of ε’, tanδ and their temperature stability was achieved in the KNN-NbZn materials and we consider this work will bring a clear understanding about the temperature-stable behaviors of dielectric properties in KNN-based ceramic capacitors.