Microstructure and properties of Bi₂O₃ doped 0.8(K_0.52Na_0.48) NbO₃–0.2KSr₂Nb₅O₁₅ lead-free ceramics

The 0.8(K_0.52Na_0.48)NbO₃–0.2KSr₂Nb₅O₁₅-yBi₂O₃ (0.8KNN-0.2KSN-yBi₂O₃) lead-free ferroelectric composite ceramics were synthesised using rod-like KSr₂Nb₅O₁₅ (KSN) and isometric (K_0.52Na_0.48)NbO₃ (KNN) particles as raw material. Effects of Bi₂O₃ doping content on microstructure, electrical, and optical properties were researched. The results indicated that the addition of Bi₂O₃ helps to densify 0.8KNN-0.2KSN-y Bi₂O₃ ceramics within limits without changing phase structure and microstructure. The dielectric constant and phase transition dispersion degree increased with the increase of Bi₂O₃ while the dielectric loss decreased. Besides, the dielectric tunability was maintained in the range of 43.7∼51.8%, and reached its maximum when Bi₂O₃ content was 1 wt%. In addition, the remnant polarisation P_r and coercive field E_c decreased with the increase of Bi₂O₃, as well as the optical transmittance of 0.8KNN-0.2KSN, but the transmittance of all samples was above 48%.