Fabrication and properties of (K_0.52Na_0.48)NbO₃–KSr₂Nb₅O₁₅ lead-free ferroelectric composite ceramics

(1 − x)(K_0.52Na_0.48)NbO₃–xKSr₂Nb₅O₁₅ [(1 − x)KNN–xKSN] lead-free ferroelectric composite ceramics were successfully prepared using KNN powders and rod-like KSN particles as raw materials. Effects of KSN content on the microstructure, electrical, and optical properties were investigated. The results showed that perovskite KNN phase and tungsten bronze KSN phase coexisted in (1 − x)KNN–xKSN ceramics, which resulted in double dielectric peaks in the temperature dependence plots. With increasing the content of KSN, the dielectric relaxor characteristic was weakened, the Curie temperature shifted to relatively lower temperature, the dielectric tunability and the optical transmittance were enhanced. 0.8KNN–0.2KSN ceramics showed the optimized electrical and optical properties, with dielectric tunability up to 45.4% at bias of 6 kV/mm, and the optical transmittance reached ~ 84% at the wavelength of near-infrared region.