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Crystal structures and ferroelectric properties of a series of Bi-layered compounds, CaBi 2 Ta 2 O 9, SrBi 2 Ta 2 O 9, and BaBi 2 Ta 2 O 9, were investigated. The structures of CaBi 2 Ta 2 O 9 and SrBi 2 Ta 2 O 9 are orthorhombic, while that of BaBi 2 Ta 2 O 9 is pseudotetragonal on the macroscopic scale but consists of microdomains with orthorhombic distortion. The ferroelectric Curie temperature of CaBi 2 Ta 2 O 9 was over 600 C, and that of SrBi 2 Ta 2 O 9 was over 300 C. BaBi 2 Ta 2 O 9, in contrast, showed relaxor-type ferroelectric behavior; that is, in the plot of temperature dependence of dielectric constant, a broad peak appeared around 60 C. As the size of the A-site cation decreases from Ba 2+ to Ca 2+, the lattice mismatch between TaO 2 and A O planes in the perovskite-type unit of A Ta 2 O 7 increases and the structural distortion becomes more pronounced. This distortion leads to the higher Curie …