2006 年 48 巻 2 号 p. 115-120
Recently, we have found a new ferroelectric barium dititanate, BaTi2O5, with a spontaneous polarization of 7μC/cm2at room temperature. The crystals, grown by a cooling method, show a ferroelectric phase transition at the Curie temperatureTcof 700-750 K, and the space group changes from monoclinicC2/mto monoclinicC2 on cooling. The dielectric constant εb' along the b-axis measured at 1 MHz reaches very large values of about 30000 atTc, while the dielectric loss tanδ remains small at values below 0.1. Thus, BaTi2O5is very promising for use in dielectric and piezoelectric devices operating at high temperatures. In this review, we would like to describe the synthetic method, the crystal structure and the physical property on the barium dititanate.