Niobium dioxide, is the chemical compound with the formula NbO2. It is a bluish-black non-stoichiometric solid with a composition range of NbO1.94-NbO2.09.[1] It can be prepared by reducing Nb2O5 with H2 at 800–1350 °C.[1] An alternative method is reaction of Nb2O5 with Nb powder at 1100 °C.[2]
The room temperature form of NbO2 has a tetragonal, rutile-like structure with short Nb-Nb distances, indicating Nb-Nb bonding.[3] The high temperature form also has a rutile-like structure with short Nb-Nb distances.[4] 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.[5]
NbO2 is insoluble in water and is a powerful reducing agent, reducing carbon dioxide to carbon and sulfur dioxide to sulfur.[1] In an industrial process for the production of niobium metal, NbO2 is produced as an intermediate, by the hydrogen reduction of Nb2O5.[6] The NbO2 is subsequently reacted with magnesium vapor to produce niobium metal.[7]
^Bolzan, A; Fong, Celesta; Kennedy, Brendan J.; Howard, Christopher J. (1994). "A Powder Neutron Diffraction Study of Semiconducting and Metallic Niobium Dioxide". Journal of Solid State Chemistry. 113 (1): 9–14. Bibcode:1994JSSCh.113....9B. doi:10.1006/jssc.1994.1334.
^Patent EP1524252, Sintered bodies based on niobium suboxide, Schnitter C, Wötting G
^Method for producing tantalum/niobium metal powders by the reduction of their oxides by gaseous magnesium, US patent 6171363 (2001), Shekhter L.N., Tripp T.B., Lanin L.L. (H. C. Starck, Inc.)
