Structural states and electrical conductivity of oxidized niobium nanopowders

The structure of niobium nanopowders (particle size 0.03–0.07 μm) oxidized in air is studied by X-ray diffraction. The nanopowder particles have a significant fraction of an amorphous phase. The amorphous component is likely to block the well-known mechanism of niobium oxidation Nb → Nbs.s → Nb6O → NbO → NbOx, which was proposed on the basis of the results of studying the oxidation of niobium powders at high temperatures. Here, Nbs.s is the solid solution of oxygen in niobium and NbOx are the higher niobium oxides NbO2 and Nb2O5. The amorphization of the surface of niobium nanopowders oxidized at 20°C can be one of the main causes of a rather high electrical resistivity (ρ ≈ 108 Θ cm) of the samples compacted from these powders.