Effects of LaFeO₃ additions on the dielectric and ferroelectric properties of (K_0.5Na_0.5)NbO₃ ceramics

Pure (K_0.5Na_0.5)NbO₃ and 0.98(K_0.5Na_0.5) NbO₃-0.02LaFeO₃ ceramics (abbreviated as KNN and 0.98KNN-0.02LF, respectively) were prepared by a solid state reaction approach, and their crystal structure, dielectric and ferroelectric properties were investigated. Pure KNN and 0.98KNN-0.02LF ceramics are the orthorhombic structure and pseudo-cubic perovskite structure, respectively. Dielectric measurements revealed that the dielectric permittivity curves of 0.98KNN-0.02LF ceramics present two anomalies compared with pure KNN: (i) The orthorhombic-tetragonal transition (T_O-T) and the tetragonal-cubic transition (T_T-C) shifts to lower temperatures. (ii) The phase transition temperature range around the temperature of the maximum dielectric permittivity (T_m) becomes more and more broad. In addition, 0.98KNN-0.02LF ceramics exhibited a very stable temperature dependence of dielectric permittivity with permittivity maximum near 2000 and dielectric loss less than 4% in the temperature range of 0-400°C. The relaxation behavior of the 0.98KNN-0.02LF ceramics is interpreted in terms of polar nanoregions (PNRs) caused by cations disorder. The P-E hysteresis loops further confirms the relaxor behavior in 0.98KNN-0.02LF ceramics.