Conductive F-doped tin dioxide sol-gel materials from fluorinated beta-diketonate tin(IV) complexes. Characterization and thermolytic behavior

Hydrolysis and condensation of (CH3COCHCOCH3)(2)SnF(Otert-Am) and (CF3COCHC OCH3)(2)Sn(Otert-Am)(2) gave soluble stannic oxo-oligomers or -polymers inc luding fluorine and beta -diketonate groups. Under thermal treatment in air at 550 degreesC, they yielded nanocrystalline fluorine-doped tin dioxide p owders. The amount of remaining ligands in the xerosols depends on the hydr olysis ratio and on the nature of the solvent used, dimethylformamide (DMF) favoring ligand removal. The thermolytic reactions have been investigated by thermogravimetry coupled to mass spectrometry: (1) the beta -diketonate ligands pyrolyze in two stages, at 200 and 320 degreesC, involving two diff erent processes; (2) elimination of polar solvents of high boiling point, s uch as DMF, occurs up to 300 degreesC; (3) fluorine is lost as fluorhydric acid from 230 degreesC. The best strategy to prepare F-doped SnO2 materials by the sol-gel route is thus to start from precursors including Sn-F bonds and to use a polar aprotic solvent of low boiling point such as acetonitri le. It led to nanocrystalline, highly conductive F-doped tin dioxide materi als with resistivities 1 order of magnitude lower than that reported for Sb -doped tin dioxide powders.