SOL-GEL ROUTE TO NIOBIUM PENTOXIDE

Niobium pentoxide powders were synthesized via the sol-gel route. Monolithic gels can be reproducibly obtained when the hydrolysis of niobium alkoxides Nb(OR)5 is performed in the presence of acetic acid. This carboxylic acid reacts with the alkoxide and leads to the formation of new Nb(OR)5-x(OAc)x (0 < x < 1) precursors. Therefore the whole hydrolysis-condensation process is modified. The different steps of the synthesis, from the molecular precursor Nb(OPent(n))5 (Pent(n) is a normal pentyl group) to the crystalline oxide were characterized by H-1 NMR, C-13 CP MAS NMR, and infrared spectroscopies, thermal analysis, and X-ray diffraction. Xerogels are obtained after drying the gel at 80-degrees-C. They are made of an oxo-polymer network in which some alkoxy groups and acetate ligands remain bonded to niobium. These organic groups are removed upon heating in air leading to the crystallization of T-Nb2O5 at around 550-degrees-C.