Characterization of vanadium diffusion barriers in Nb-Sn composite wires

Ductile vanadium has been explored for use as a diffusion barrier material in niobium-tin composite wires. Vanadium is found to co-process well, standing over 99.995% area reduction without anneal. Resistance ratios greater than 300 to 1 (0°c to 20K) have been measured in reacted composite wire with noncopper current densities greater than 1700 A/mm²at 10 Tesla, 4.2K. Vanadium forms an intermetallic compound on the tin side which should not be superconducting above 4.2K. The composite residual resistance ratio (RRR) is seen to be dependent on reaction conditions being higher as the reaction temperature is dropped. To determine the source of this effect a copper-vanadium composite was fabricated. Features similar to the superconducting wire were observed. There is a reasonable overlap of reaction conditions suitable for both the superconductor and the copper making high RRR possible for optimized conductors.