Synthesis of ɛ-NbN and δ-NbN by metathesis reaction of NaNbO3 and BN

Abstract δ-NbN powder with particles of ∼1 µm in size was obtained by heating a mixture of NaNbO3 and BN powders at 1373 K for 1 h, while agglomerates composed of ɛ-NbN platelet grains up to 50 µm in size were obtained by heating the mixture at the same temperature for 10 h. Metathesis reaction in which sodium borate was formed with replacement of the oxygen and nitrogen from NaNbO3 and BN occurred with the NbN formation. Wavelength-dispersive X-ray analysis showed that the molar ratios of Nb to N in the synthesized δ-NbN and ɛ-NbN were ∼1:1. Magnetic susceptibility measurements showed that the δ-NbN powder was a superconductor with a transition temperature of ∼16 K. In comparison, the ɛ-NbN agglomerates did not exhibit superconductivity above 2 K.