Magnesium diboride superconducting wires and bulk samples synthesized at high pressure were produced with a variety of reactive metal additions. All of the samples exhibited high critical current densities, but particular attention was paid here to the striking observation that reactive metal additions such as Ti substantially improved the critical current values, but had little detrimental effect on TC values. For instance, the critical current values in the wires could be increased by more than a factor of 3.5 at 4 K and 10 T by the inclusion of up to 10wt%Ti. In bulk materials the JC values could be increased by even larger values, and the irreversibility field at 20K increased to above 7T. In a detailed study of the microstructure of these materials it was shown that powder-in-tube ex situ wires with 10wt%Ti additions have a complicated layered microstructure around the Ti-rich particles, possibly forming Ti–B phases, but also incorporating impurity elements including H. X-ray diffraction data, TEM and elemental mapping in the Nano-secondary ion mass spectrometry confirmed the surprising suggestion that samples synthesized at high pressure from Mg and B with Ti additions contain a titanium hydride. These new compositional data support the idea that reactive metal additions were extremely beneficial in MgB2 wires and bulk materials because they preferentially adsorb deleterious impurities from the superconducting matrix.

Chemical Interactions in Ti-Doped MgB2 Superconducting Bulk Samples and Wires. S.Haigh, P.Kovac, T.A.Prikhna, Y.M.Savchuk, M.R.Kilburn, C.Salter, J.Hutchison, C.Grovenor: Superconductor Science and Technology, 2005, 18, 1190-6