Preparation and properties of multifilament niobium carbonitride superconductor

The preparation and characterization of a multifilament niobium carbonitride yarn is reported here for the first time. The fine diameter multifilament yarn was prepared by chemical conversion of a precursor carbon yarn. The fibers are generally composed of both NbC and NbCN phases and exhibit a T
c
of 16-17.5°K and an H
c2
of 110- 120kG. I
c
values at zero field of up to 130 amperes have been measured corresponding to a J
c
of 10
⁶
A/cm
²
. I
c
is proportional to the amount of superconductor phase present as judged by weight gain data. At low conversion levels an anomaly has been detected in critical current behavior of the fibers suggesting a non-continuous superconducting path. Electrical contact to the fibers by copper coating is discussed showing the importance of obtaining a low resistance contact. J
c
was measured as a function of magnetic field for both the pure material and samples doped with silicon using SiCl
4
. The silicon dopant was found to be effective in reducing the field dependence of the critical current.