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Stabilization of a perovskite-type solid solution (1−x) PbTiO3–x BiScO3 with x⩾0.45 was demonstrated by high-pressure synthesis, and the phase diagram and the ferroelectric properties of the solid solution were investigated. The crystal symmetry of the perovskite subcell change in turn from tetragonal, to rhombohedral, to pseudocubic, to monoclinic, and then to triclinic as x increases. It was found that the tetragonal, rhombohedral, and pseudocubic phases are ferroelectric, while the monoclinic phase is not. In the morphotropic phase boundary in the vicinity of x=0.37 between tetragonal and rhombohedral phases, the maximum electromechanical coupling factor and the minimum coercive electric field were just like those observed in other Pb-based ferroelectric perovskites. In addition, relaxor behavior in the dielectric constant was observed in the vicinity of x=0.5.

Rhombohedrally distorted perovskite BiFeO 3 ­K 0.5 Na 0.5 NbO 3 ceramics with ferroelectricity and ferromagnetism were synthesized by solid-state reaction. The effect of K 0.5 Na 0.5 NbO 3 content on the crystal structure, electrical and magnetic properties of a BiFeO 3 ­K 0.5 Na 0.5 NbO 3 system was examined with a view to achieving multiferroic BiFeO 3-based ceramics. Perovskite BiFeO 3 ­ K 0.5 Na 0.5 NbO 3 single phase was obtained by formation of solid solution with K 0.5 Na 0.5 NbO 3 , whereas pure BiFeO 3 ceramics contained a small amount of a second phase, such as Bi 36 Fe 2 O 57. The crystallographic symmetry of BiFeO 3 ­K 0.5 Na 0.5 NbO 3 changed from rhombohedral to cubic when the content of K 0.5 Na 0.5 NbO 3 exceeded 15 mol %. The rhombohedrally distorted BiFeO 3 ­K 0.5 Na 0.5 NbO 3 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.

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