Preparation of Na_<0.5>Bi_<0.5>TiO_3 by hydrothermal reaction

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Perovskite-type Na_<0.5>Bi_<0.5>TiO_3 was prepared by hydrothermal reaction using TiO_2 (anatase) and Bi_2O_3 in NaOH solution. A single phase of Na_<0.5>Bi_<0.5>TiO_3 was obtained when the molar ratio of NaOH/TiO_2 was above 60 and the reaction temperature was above 180℃. In the temperature range from 220 to 300℃ large crystals of Na_<0.5>Bi_<0.5>TiO_3 were obtained. The maximum dimension of crystals was 〜1.0×1.0×1.0mm which were obtained under the condition of NaOH/TiO_2=60 at 260℃ for 2d. The TG-curve of large crystals showed a mass loss of 0.25mass% which was caused by release of OH group. The chemical composition for large crystals of Na_<0.5>Bi_<0.5>TiO_3 was found to be Na_<0.50>Bi_<0.45>H_<0.05>TiO_<3->. The X-ray powder diffraction pattern of large crystals was indexed with the cubic cell of the lattice parameter of a=3.891(1) Å and the cubic phase decomposed to the compound with the hexagonal cell of a=5.4889(7) and c=13.423(2) Å and a small amount of an unknown phase at >1000℃. The samples heated at 1180℃ exhibited the Curie point at approximately 330℃ and the P-E and S-E hysteresis loops.
社団法人日本セラミックス協会の論文
2008-11-01