Conductive F-doped Tin Dioxide Sol−Gel Materials from Fluorinated β-Diketonate Tin(IV) Complexes. Characterization and Thermolytic Behavior

Hydrolysis and condensation of (CH 3 COCHCOCH 3 ) 2 SnF(O tert -Am) and (CF 3 COCHCOCH 3 ) 2 Sn(O tert -Am) 2 gave soluble stannic oxo-oligomers or -polymers including fluorine and β-diketonate groups. Under thermal treatment in air at 550 °C, they yielded nanocrystalline fluorine-doped tin dioxide powders. The amount of remaining ligands in the xerosols depends on the hydrolysis 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 β-diketonate ligands pyrolyze in two stages, at 200 and 320 °C, involving two different processes; (2) elimination of polar solvents of high boiling point, such as DMF, occurs up to 300 °C; (3) fluorine is lost as fluorhydric acid from 230 °C. The best strategy to prepare F-doped SnO 2 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 acetonitrile. It led to nanocrystalline, highly conductive F-doped tin dioxide materials with resistivities 1 order of magnitude lower than that reported for Sb-doped tin dioxide powders.