Preparation of Na0.5Bi0.5TiO3 by hydrothermal reaction

Perovskite-type Na0.5Bi0.5TiO3 was prepared by hydrothermal reaction using TiO2 (anatase) and Bi2O3 in NaOH solution. A single phase of Na0.5Bi0.5TiO3 was obtained when the molar ratio of NaOH/TiO2 was above 60 and the reaction temperature was above 180°C. In the temperature range from 220 to 300°C large crystals of Na0.5Bi0.5TiO3 were obtained. The maximum dimension of crystals was ~1.0 × 1.0 × 1.0 mm which were obtained under the condition of NaOH/TiO2 = 60 at 260°C for 2 d. The TG-curve of large crystals showed a mass loss of 0.25 mass% which was caused by release of OH group. The chemical composition for large crystals of Na0.5Bi0.5TiO3 was found to be Na0.50Bi0.45H0.05TiO3. 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°C. The samples heated at 1180°C exhibited the Curie point at approximately 330°C and the P-E and S-E hysteresis loops.