Short-range dissolution–precipitation crystallization of hydrothermal barium titanate

A modified autoclave was used to investigate the crystallization mechanism of BaTiO3 during the hydrothermal reaction of Ba(OH)2 and TiO2 anatase. An uneven distribution of the crystallized BaTiO3 particles was observed: more than 99 wt.% of total BaTiO3 particles remained where the precursor TiO2 was put; less than 1 wt.% was collected from the areas away from the TiO2. According to the experimental observations in this work and proofs reported in the literature, we propose that the crystallization mechanism is dissolution–precipitation in nature, but the soluble Ti4+ species can only redisperse in a short distance away from TiO2 particles before precipitation. In other words, the nucleation of hydrothermal BaTiO3 starts at a low concentration of Ti4+. The mechanism of the Ba(OH)2–Ti(OH)4 reaction is a fast dehydration process.