Effects of LaFeO₃ Additions on the Dielectric and Ferroelectric Properties of (K_0.5Na_0.5)NbO₃ Ceramics

Pure (K0.5Na0.5)NbO3 and 0.98(K0.5Na0.5)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 struc- ture and pseudo-cubic perovskite structure, respectively. Dielectric measurements revealed that the dielectric permit- tivity curves of 0.98KNN-0.02LF ceramics present two anomalies compared with pure KNN: (i) The orthorhombic- tetragonal transition (TO-T) and the tetragonal-cubic transition (TT-C) shifts to lower temperatures. (ii) The phase transi- tion temperature range around the temperature of the maximum dielectric permittivity (Tm) becomes more and more broad. In addition, 0.98KNN-0.02LF ceramics exhibited a very stable temperature dependence of dielectric permittiv- ity with permittivity maximum near 2000 and dielectric loss less than 4% in the temperature range of 0-400℃. 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.