The effect of the hydrothermal synthesis variables on barium titanate powders

In this work, the influence of (a) Ba excess in the starting hydrothermal mixture with TiO2, (b) hydrothermal reaction temperature, and (c) washing cycles on the hydrothermal synthesis of barium titanate (BaTiO3) were investigated to assess their relative contributions to the final characteristics of the sintered oxide. BaTiO3 cake was prepared by hydrothermal synthesis at 150 °C and 180 °C using BaOH2·8H2O and TiO2·xH2O as starting hydrothermal mixture with an excess of Barium (+1 Ba mol% and +2 Ba mol%). The obtained BaTiO3 cake was washed several times from 0 to 14 (Wn<15) using simple de-ionized water and then sintered at 1120 °C for 3 h. All considered hydrothermal syntheses variables strongly contribute to the final characteristics of the sintered BaTiO3 powders in terms of Ba2+/Ti4+ molar ratio, crystalline structure and mean particle size. In particular, it is clear from these experiments that the removal of the unfavorable barium salts from BaTiO3 cake by long washing cycles before final calcination is a critical step in the hydrothermal synthesis of BaTiO3.