Tetragonal niobium sub-oxides, NbOx and NbOz (Nb3O), were grown via the solid-state oxidation of metallic niobium at 360 and 390C, respectively. Electron microscopy and diffraction were used to identify the lattice correspondence between the sub-oxides and the niobium solid-solution matrix. The twinned structure of NbOx permitted the determination of the interface energy of the twin planes, which were found to range from 22 to 28mJ/m2.

Croissance Orientée des Sous Oxydes de Niobium dans la Matrice de Niobium. Y.Monfort, A.Maisseu, G.Allais, A.Deschanvres: Journal of Crystal Growth, 1972, 13-14[C], 829-33