Synthesis and Lattice Distortion of Ferroelectric/Antiferroelectric Bi(III)-containing Perovskites

摘要

Bi(III)-containing perovskites Bi_(1/2)Ag_(1/2)TiO_3 and Bi(M_(1/2)Ti_(1/2))O_3 (M= Co, Mg, and Ni) were synthesized under oxygen pressure as high as approximately 1 MPa and under a pressure as high as 6 GPa, and the lattice distortions were investigated. It was found that ferroelectric Bi_(1/2)Ag_(1/2)TiO_3 may be rhombohedrally distorted. In constrast, Bi(M_(1/2)Ti_(1/2))O_3 (M= Co, Mg, and Ni), the structure of which is different from GdFeO_3-type compound, is monoclinically distorted. The ratio of lattice parameters of the monoclinic perovskite-subcell for Bi(M_(1/2)Ti_(1/2))O_3 (M= Co, Mg, and Ni), a_m/b_m is larger than that of GdFeO_3-type perovskites, though the tolerance factor is close. In addition, it was found that Bi(Ni_(1/2)Ti_(1/2))O_3 undergoes a first-order phase transition from a GdFeO_3-type phase(high-temperature phase) at around 490 K. These results indicate that the Bi~(3+) character in Bi(III)-containing perovskites strongly influences the structure distortion.