The structural, morphological, C content and
TC
changes of the NbC superconductor prepared by Nb powder and carbon
nanotubes have been investigated. Our results indicate that high quality NbC
superconductor can be obtained using Nb powder and carbon nanotubes as starting
materials without the addition of iodine as a transport agent. The determined
TC and upper
critical field HC2(0)
for the typical NbC superconductor prepared at
1100 °C are
TC (R = 0) = 10.6 K,
TC (M = onset) = 11.4 K and
HC2(0) = 1.57 ± 0.15 T, respectively. The
lattice parameter, TC
and C content of the prepared samples increase with increasing synthesis temperature in the temperature range
850–1030 °C, and then remain
constant in the range 1030–1100 °C.
Magnetic relaxation rate, critical current density and transport properties have been investigated on MgB2 bulks from 1.6 K to Tc at magnetic fields up to 8 T. A vortex phase diagram is depicted based on these measurements. A large separation between the bulk irreversibility field Hirr(T) and the upper critical field Hc2(T) has been found. It is thus proposed that there is a quantum vortex liquid due to strong quantum fluctuation of vortices at 0 K. It is also found that the magnetic relaxation rate is weakly dependent on temperature but strongly dependent on field indicating a trivial influence of thermal fluctuation on the vortex depinning process. Therefore, the phase line Hirr(T) is attributed to quantum vortex melting in the rather clean system at a finite temperature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.