Structure and superconductivity of MgB_2-carbon nanotube composites

摘要

It has been reported that MgB_2 lostits superconductivity when doped with 40 at.% Al. Here, we report on the influence of carbon nanotubes (CNTs) on the structure and superconductivity of MgB_2-CNTs composites. The lattice parameters of MgB_2 with 10 at.% CNTs are a = 0.30815 nm and c = 0.35322 nm, slightly different from those of the pure MgB_2, which indicates that carbon atoms may have substituted boron atoms in MgB_2. The transition temperature of the samples decreases as the CNTs content increases. However, the samples added with about 40 at.% CNTs still have a transition temperature of 24 K. When added with bulk CNTs (between 20 and 40 at.%), the samples present a semiconductor behavior in the high-temperature region (above 40 K) and have superconductivity at low temperatures (below 32 K).