NITRIDE FORMATION BY AIR IGNITION

It was recently reported that a new barium-niobium oxide, prepared by the ignition in air of a mixture of barium peroxide and niobium metal powders, was superconducting below temperatures of about 20 K. This finding, if true, would be of considerable significance because the highest superconducting transition temperature (T-c) previously found for a niobium-based oxide is 5.5 K. We have reproduced this synthesis, and we conclude from X-ray diffraction, electron microprobe, and magnetic susceptibility studies that the superconducting phase in this product is basically niobium nitride. Ignition of niobium metal powder in air leads only to niobium oxide, but ignition in air of Ta plus BaO2 leads to the formation of Ta2N. Apparently, there have been no previous reports of nitride formation by any ignition reaction in air. (C) 1995 Academic Press, Inc.