The reduced niobium oxides Nb25O62, Nb47O116, Nb22O54, and Nb12O29 have been prepared in pure polycrystalline form by a niobium-metal gettering technique. They are related to the high niobia parent structure through the action of cystallographic shear to accommodate oxygen deficiency in Nb2O5-delta. Electrical conductivities increase with increasing reduction: Nb12O29 is a metallic conductor down to 0.3 K. All show, surprisingly, Curie-Weiss behavior in the chi-vs-T curves, with Nb12O29 ordering antiferromagnetically at 12 K.
Cava, R. J., Batlogg, B., Krajewski, J. J., Poulsen, H. F., Gammel, P., Peck Jr., W. F., & Rupp Jr., L. W. (1991). Electrical and magnetic properties of Nb2O5-γ crystallographic shear structures. Physical Review B, 44(13), 6973-6981. https://doi.org/10.1103/PhysRevB.44.6973