Superconductivity in MgB2 doped with Ti and C

Measurements of the superconducting upper critical field, Hc2, and critical current density, Jc, have been carried out for MgB2 doped with Ti and/or C in order to explore the problems encountered if these dopants are used to enhance the superconducting performance. Carbon replaces boron on the MgB2 lattice and apparently shortens the electronic mean free path of MgB2 and raising Hc2. Titanium forms precipitates of either TiB or TiB2 that enhance the flux pinning and raise Jc. Most of these precipitates are intra-granular in the MgB2 phase. For samples containing both C and Ti doping, the C appears to still replace B in the MgB2 lattice and the Ti precipitates out as a boride. If approximately 0.5%Ti and approximately 2%C are co-deposited with B to form doped boron fibers and these fibers are in turn reacted in Mg vapor to form doped MgB2, the resulting superconductor has μ0Hc2(T = 0) ∼ 25 T and Jc ∼ 10,000 A/cm2 at 5 K and 2.2 T.