The reduced niobium oxides ${\mathrm{Nb}}_{25}$${\mathrm{O}}_{62}$, ${\mathrm{Nb}}_{47}$${\mathrm{O}}_{116}$, ${\mathrm{Nb}}_{22}$${\mathrm{O}}_{54}$, and ${\mathrm{Nb}}_{12}$${\mathrm{O}}_{29}$ 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 ${\mathrm{Nb}}_2$${\mathrm{O}}_{5\mathrm{-}\mathrm{\delta }}$. Electrical conductivities increase with increasing reduction: ${\mathrm{Nb}}_{12}$${\mathrm{O}}_{29}$ is a metallic conductor down to 0.3 K. All show, surprisingly, Curie-Weiss behavior in the χ-vs-T curves, with ${\mathrm{Nb}}_{12}$${\mathrm{O}}_{29}$ ordering antiferromagnetically at 12 K.

• Received 28 May 1991

DOI:https://doi.org/10.1103/PhysRevB.44.6973