Soft-Chemistry Synthesis and Characterization of Bismuth Oxyfluorides and Ammonium Bismuth Fluorides.

Two bismuth oxyfluorides, BiOF and BiO_0.5F₂, have been prepared by soft chemistry. These two compounds are of interest for application as new type of positive electrode active materials in secondary lithium battery. BiOF was obtained directly from the fluorination of Bi₂O₃ by a saturated aqueous solution of NH₄F. BiO_0.5F₂ was obtained by the hydrolysis of β-NH₄BiF₄ at 70°C. The ammonium bismuth fluoride β-NH₄BiF₄, which is a new orthorhombic form of NH₄BiF₄, was obtained by reacting BiF₃ in a saturated aqueous solution of NH₄F. Two other ammonium bismuth fluorides, (NH₄)_0.5BiF_3.5 and NH₄Bi₃F₁₀, were also prepared by annealing β-NH₄BiF₄ at a relatively low temperature under inert atmosphere. The existence of the fluorite (NH₄)_0.5BiF_3.5 is reported for the first time in this paper. [ABSTRACT FROM AUTHOR]