A low-temperature hydrothermal synthesis of submicron spherical BaF₂

The sub-micron spherical barium fluoride (BaF₂) was successfully synthesized via a low-temperature hydrothermal method using ethylenediamine tetraacetic acid disodium salt (EDTA-2Na) as the chelating agent. The effect of pH, the molar ratio of EDTA to Ba²⁺, barium hydroxide octahydrate (Ba(OH)₂·8H₂O) concentration, hydrofluoric acid (HF) concentration, hydrothermal temperature and time, on the formation of spherical BaF₂ were investigated. The formation mechanism of spherical BaF₂ has been proposed based on the experimental results. The results show that the spherical BaF₂, with an average size of 346.9 nm, is formed by the self-assembly of nanocubes. The optimized synthesis conditions are: pH = 14, EDTA-2Na : Ba²⁺ = 1 : 1, Ba(OH)₂ concentration is 0.1 mol L^-1, HF concentration is 2.0 mol L^-1, hydrothermal temperature is 80 °C and hydrothermal time is 2.0 h. The self-assembly mechanism of the spherical secondary structure was revealed from the perspective of crystal nucleation and growth, and the important role of EDTA in the spherical BaF₂ formation is explained.