A novel sol-gel process for silica/fluoride composites is described. Crystallization of LaF3 in the sol-gel silica has been investigated. Dry silica gels containing La3+ and trifluoroacetate ions (CF3COO-) were produced from tetramethylorthosilicate (TMOS), methanol, dimethylformamide, lanthanum acetate, trifluoroacetic acid, water and nitric acid. By heating the gels at temperatures above 300 °C, LaF3 microcrystals with a size of 10-30 nm were formed in the silica matrix. IR, XPS and TG-DTA analyses suggested that CF3COO- ions are coordinated to La3+ ions in the sols and the dried gels, leading to the formation of LaF3 by the thermal decomposition at elevated temperatures.
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