Preparation of a new pyrochlore-type compound Na0.32Bi1.68Ti2O6.46(OH)0.44 by hydrothermal reaction

A new pyrochlore-type Na0.32Bi1.68Ti2O6.46(OH)0.44 with the cubic cell of a=10.339(5) Å was prepared by hydrothermal reaction using TiO2 (anatase) and Bi2O3 in NaOH solution. This compound was obtained when the molar ratio of NaOH/TiO2 was above 2 and the reaction temperature was above 240 °C. The TG-curve of as-prepared sample showed a mass loss of 0.8 mass% which was caused by release of OH group. This compound decomposed to a pyrochlore-type compound and a layered-type Na0.5Bi4.5Ti4O15 above 800 °C. The optical band gap of Na0.32Bi1.68Ti2O6.46(OH)0.44 was estimated to be 2.5 eV.