Synthesis and Lattice Distortion of Ferroelectric/Antiferroelectric Bi(III)-containing Perovskites
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Synthesis and Lattice Distortion of Ferroelectric/Antiferroelectric Bi(III)-containing Perovskites Yoshiyuki Inaguma*, Atsushi Miyaguchi, and Tetsuhiro Katsumata Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo, 171-8588, Japan ABSTRACT Bi(III)-containing perovskites Bi1/2Ag1/2TiO3 and Bi(M1/2Ti1/2)O3 (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 Bi1/2Ag1/2TiO3 may be rhombohedrally distorted. In constrast, Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), the structure of which is different from GdFeO3-type compound, is monoclinically distorted. The ratio of lattice parameters of the monoclinic perovskite-subcell for Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni), am/bm is larger than that of GdFeO3-type perovskites, though the tolerance factor is close. In addition, it was found that Bi(Ni1/2Ti1/2)O3 undergoes a first-order phase transition from a GdFeO3-type phase(high-temperature phase) at around 490 K. These results indicate that the Bi3+ character in Bi(III)-containing perovskites strongly influences the structure distortion. INTRODUCTION Much attention has been recently paid to perovskite-type(formula ABO3) and related oxides such as Bi1/2Na1/2TiO3 that contain Bi3+ as the A-site cation[1], primarily due to their ferroelectricity (FE) and antiferroelectricity (AFE). Because Bi3+ and Pb2+ ions have the same electronic configuration (6s)2, FE and AFE in Bi3+ compounds are thought to be induced by the hybridization between the (6s)2 and 2p orbitals of oxygen, the same as in Pb2+ compounds[1]. Furthermore, Nakamura et al. have proposed that the mass-inequality between A-site ions containing heavy Bi and BO3 evokes an anharmonicity of the phonon vibration related to the Last mode(A-BO3), producing ferroelectricity[2]. Due to the lower structural stability of Bi3+-containing perovskite(BiBO3) under ambient conditions than of Pb2+-containing perovskite(PbBO3), originating from the smaller ionic radius of Bi3+ than Pb2+[3], i.e. a smaller tolerance factor, there have been fewer studies of Bi3+-containing perovskites. To be able to discuss FE and AFE in more detail, it is important to synthesize novel Bi-containing perovskites and to investigate their structures and dielectric properties. On the other hand, stabilization of the Bi-containing perovskite phase has been demonstrated using high pressure and oxygen pressure. It has been reported that BiMO3 (M=Mn, Cr [4], Sc, Ni, Co, Y[5] ) can be synthesized under pressures as high as 4-7 GPa. We have recently synthesized the following perovskites: Bi1/2Ag1/2TiO3 under oxygen pressures as high as approximately 1 MPa [6], and Bi(Ni1/2Ti1/2)O3 under pressures as high as 6 GPa[7]. The former appears to be ferroelectric, and the latter anti-ferroelectric. In the present study, Bi(III)-containing perovskites Bi1/2Ag1/2TiO3 and Bi(M1/2Ti1/2)O3 (M= Co, Mg, and Ni) were synthesized, an
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