Niobium Dioxide, NbO₂

Like the sesquioxide, Niobium Dioxide, NbO₂, is obtained by reducing the pentoxide with hydrogen at a high temperature. It has also been prepared by the electrolysis of fused potassium niobium oxyfluoride, K₂NbOF₅, in a platinum vessel, which acts as the cathode, and using an anode of the same material. Niobium dioxide is a black powder which is stable in air at ordinary temperatures; on being heated in air it forms the white pentoxide. It is not attacked by hot or cold acids, including hydrofluoric acid and aqua-regia; boiling potassium hydroxide solutions dissolve it slowly. Its crystal structure has been studied by Goldschmidt.