Niobium dioxide, is the chemical compound with the formula NbO<sub>2</sub>. It is a bluish-black non-stoichiometric solid with a composition range of NbO<sub>1.94</sub>-NbO<sub>2.09</sub>. It can be prepared by reducing Nb<sub>2</sub>O<sub>5</sub> with H<sub>2</sub> at 800âÂÂ1350 ðC. An alternative method is reaction of Nb<sub>2</sub>O<sub>5</sub> with Nb powder at 1100 ðC.
The room temperature form of NbO<sub>2</sub> has a tetragonal, rutile-like structure with short Nb-Nb distances, indicating Nb-Nb bonding. The high temperature form also has a rutile-like structure with short Nb-Nb distances. Two high-pressure phases have been reported: one with a rutile-like structure (again, with short Nb-Nb distances); and a higher pressure with baddeleyite-related structure.
NbO<sub>2</sub> is insoluble in water and is a powerful reducing agent, reducing carbon dioxide to carbon and sulfur dioxide to sulfur. In an industrial process for the production of niobium metal, NbO<sub>2</sub> is produced as an intermediate, by the hydrogen reduction of Nb<sub>2</sub>O<sub>5</sub>. The NbO<sub>2</sub> is subsequently reacted with magnesium vapor to produce niobium metal.