Sol-gel synthesis of inorganic complex fluorides using trifluoroacetic acid

A sol-gel method to prepare inorganic complex fluorides, SrAlF₅ and BaMgF₄ is described. Metal acetates and alkoxide were used as starting materials, and trifluoroacetic acid was used as a fluorine source. The formation of the fluorides was examined using thermal analysis, X-ray diffraction (XRD) and infrared (IR) absorption. The fluorides were formed through the highly exothermic decomposition reaction of trifluoroacetate gels at temperatures around 321-339°C. The heating time necessary to produce SrAlF₅ and BaMgF₄ powder samples was considerably reduced in the sol-gel process as compared to the solid-state reaction between SrF₂ and AlF₃ or BaF₂ and MgF₂. It is also shown that BaMgF₄ thin films could be prepared by the sol-gel process using a spin-coating technique. The characteristics of the films were investigated with a field emission scanning electron microscope and a spectrophotometer.