Preparation and superconducting properties of MoN and MoC in form of wires

Methods for the preparation of MoN and MoC in form of wires by diffusion of N and C, resp. into Mo wires of 0.5 mm in diameter at high temperatures have been developed. MoN samples were made by heating the Mo wires at temperatures between 750 and 950°C in a stream of ammonia gas under atmospheric pressure, whereas MoC samples were prepared by heating the Mo wires at temperatures between 1900 and 2160°C in a methane gas stream under low pressure between 10 and 20 Torr. MoN crystallizes in the hexagonal WC type structure, but MoC prefers as many of these interstitial compounds the cubic NaCl type lattice. Both materials show fairly sharp transitions to superconductivity at temperatures (midpoints of the transition curves) of 12.95 K for MoN and 12.22 K for MoC. The composition of the samples has been controlled by microprobe analysis.