High T_m lead-free relaxor ferroelectrics with broad temperature usage range: 0.04 BiScO₃ -0.96 (K_0.5 Na_0.5) NbO₃

In order to develop high temperature lead-free relaxors, x BiScO3 - (1-x) (K0.5 Na0.5) NbO3 [xBS- (1-x) KNN] ceramics were proposed using a tolerance factor approach. To verify this proposal, xBS- (1-x) KNN ceramics were synthesized by conventional solid-state sintering. A stable perovskite phase was obtained when KNN content was greater than 96 mol %. The diffuse phase transition and frequency dispersion of the dielectric constant, which are two typical characteristics of relaxor ferroelectrics, were observed in xBS- (1-x) KNN ceramics. The dielectric relaxor behavior follows a modified Curie-Weiss law relationship. In addition, 0.04BS-0.96KNN ceramics show a broad and stable permittivity maximum near 2500 from 100 to 300 °C and lower dielectric loss (<5%) at broad temperature usage range (100-300 °C). The results indicate that this material may have great potential for high temperature capacitors in automobile applications.