SINGLE-WALL CARBON NANOTUBES ADDITION EFFECTS ON THE SUPERCONDUCTING PROPERTIES OF MgB2

In this work we describe the effects of adding different amount of single-wall (sw) carbon nanotubes (CNT) on the superconducting properties of MgB2. We observed that the amount of swCNT that partially dilute into the MgB2 matrix is lower than for double-wall (dw) CNT samples for the same nominal content. This C incorporation leads to an increase of the upper critical field (H-c2), with a maximum H-c2(0) extrapolated value of 33.5 T, expected for a two-gap superconductor in the dirty limit. At the same time, the fraction of swCNT that has not been incorporated into MgB2 lattice may retain their structural integrity acting as strong vortex pinning centers. In this case the optimum nominal swCNT content for increasing critical current density (J(c)) is in the range 7.5-10%at.