Chemical Precipitation of BaSn(OH)6 and Its Thermal Destruction in the Process of BaSnO3 Preparation

The synthesis of barium hexahydroxostannate BaSn(OH)₆ and its thermal destruction leading to the barium stannate BaSnO₃ have been studied. It is shown that the most intensive decomposition of BaSn(OH)₆ occurs in the temperature range of 200–650°C. Crystallization of BaSnO₃ proceeds in a narrow temperature range (650–675°C), and the maximum of the corresponding exo-effect is located at 667°C. It was found that at 500°C (within 60 min) BaSn(OH)₆ completely decomposes with the formation of X-ray amorphous powder. When the material is kept at 600°C (60 min), crystallization of barium stannate BaSnO₃ with perovskite structure takes place. The crystalline impurity of barium carbonate contained in the semiproduct is preserved up to 600°C, and at temperatures from 700°C the single-phase BaSnO₃ is formed. The crystallization temperature of barium stannate can be reduced by 50–75°C due to thermal exposure of the powder for 40–60 min. Holding the semiproduct at 600°C for 60 min forms barium stannate with an average crystallite size of 21 ± 2 nm, and at 700°C there is a slight increase in this parameter (up to 22 ± 2 nm). With increasing temperature up to 1000°C there is intensification of crystallite enlargement process (up to 34 ± 3 nm). The obtained BaSnO₃ powder, according to scanning electron microscopy data, consists of microrods (average length is about 85 μm; average diameter is about 10 μm). The surface of the rods is partially covered with spherical particles formed from smaller primary particles of about 30 nm in size.