The Study Of Structure And Properties On KNN Lead-Free Piezoceramics

The use of lead-based ceramics results in the formation of high toxicity of lead oxide,which is harmful to human health and environment.Therefore,it is very important to use lead-free piezoelectric materials for environmental protection.Sodium potassium niobate K_xNa_1-xNbO₃?KNN?,a possible candidate for replacing Pb(Zr_xTi_1-x)O₃?PZT?in piezoelectric devices,is appealing in piezoelectric applications because of its relatively low dielectric permittivity,large electromechanical coupling factors,very high Curie temperature?about 420°C?and good ferroelectric properties?P_r=33 ?C/cm²?.Compositional modification is one of the ways to improve the piezoelectric properties of KNN-based ceramics,which reducing the orthorhombic-tetragonal phase transition temperature(T_O-T),forming coexistence of the tetragonal and orthorhombic phases at room temperature.In our study,the?1-x?KNN-xCaZrO₃?SrTiO₃?BaZrO₃???1-x-y?KNN-xBaZrO₃-y(Bi_0.5Li_0.5)TiO₃ ? 0.94KNN-?0.06-x?LiSbO₃-xBi_0.5(Na_0.82K_0.18)0.5ZrO₃ and 0.94KNN-?0.06-x?LiSbO₃-x(Bi_0.5Ag_0.5)ZrO₃ system were prepared by solid reaction method,to improve the dielectric,and piezoelectric properties of KNN-based ceramics.Results showed that samples in those system have a intact process of phase structure evolution and a mixed phase region.In this region,enhanced electrical properties were obtained.In?1-x-y?KNN-xBaZrO₃-y(Bi_0.5Li_0.5)TiO₃ system,the excellent properties d₃₃ = 185 p C/N,kp = 41.5% were located at x=0.06 and y=0.02?In0.94KNN-?0.06-x?Li Sb O₃-x Bi_0.5(Na_0.82K0.18)0.5Zr O₃ system,the excellent properties d₃₃ = 185pC/N,d₃₃* = 227pm/V,k_p = 34% were located at x=0.025 ? In0.94KNN-?0.06-x?LiSbO₃-x(Bi_0.5Ag_0.5)ZrO₃ system,the excellent properties d₃₃ =225pC/N,d₃₃* = 275pm/V,k_p = 42% were located at x=0.025 ? The approach of two-step sintering obviously broadened the sintering temperature range of the ceramics and further improved piezoelectric properties by ¹5%,indicating it is a promising way for fabricating KNN-based ceramics.Moreover,in0.94KNN-?0.06-x?LiSbO₃-x(Bi_0.5Ag_0.5)ZrO₃ system,all studied samples showed good resistance to thermal depoling up to temperatures close to their Curie points,suggesting that this system should be an attractive lead-free material system for piezoelectric applications.