Niobium dioxide
# Niobium dioxide

Niobium dioxide, is the chemical compound with the formula $NbO_2.$ It is a bluish-black non-stoichiometric solid with a composition range of $NbO_{1.94}-NbO_{2.09}.$ It can be prepared by reducing $Nb_2O_5$ with $H_2$ at 800–1350 °C. An alternative method is reaction of $Nb_2O_5$ with Nb powder at 1100 °C.

## Properties

The room temperature form of $NbO_2$ 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.

$NbO_2$ 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, $NbO_2$ is produced as an intermediate, by the hydrogen reduction of $Nb_2O_5.$ The $NbO_2$ is subsequently reacted with magnesium vapor to produce niobium metal.

