Synthesis and properties of perovskite BiFeO₃–K_0.5Na_0.5NbO₃ ceramics by solid-state reaction

Abstract

Rhombohedrally distorted perovskite BiFeO₃–K_0.5Na_0.5NbO₃ ceramics with ferroelectricity and ferromagnetism were synthesized by solid-state reaction. The effect of K_0.5Na_0.5NbO₃ content on the crystal structure, electrical and magnetic properties of a BiFeO₃–K_0.5Na_0.5NbO₃ system was examined with a view to achieving multiferroic BiFeO₃-based ceramics. Perovskite BiFeO₃–K_0.5Na_0.5NbO₃ single phase was obtained by formation of solid solution with K_0.5Na_0.5NbO₃, whereas pure BiFeO₃ ceramics contained a small amount of a second phase, such as Bi₃₆Fe₂O₅₇. The crystallographic symmetry of BiFeO₃–K_0.5Na_0.5NbO₃ changed from rhombohedral to cubic when the content of K_0.5Na_0.5NbO₃ exceeded 15 mol %. The rhombohedrally distorted BiFeO₃–K_0.5Na_0.5NbO₃ showed a high Curie temperature (>770°C) and weak ferromagnetism at room temperature. Dielectric properties of the resultant ceramics were improved by controlling the amount of Mn doping to facilitate ferroelectric measurements.