The MgB 2 -based material high-pressure synthesized at 2 GPa and 800 o C for 1 h from Mg and B (taken in the stoichiometry ratio of MgB 2 ) with addition of 2-10 wt% of Ti demonstrated the critical current density (j c ) higher than 100 kA/cm 2 at 33 K in 0 T field and at 20 K up to 3 T. At 20 K the critical current density higher than 10 kA/cm 2 was observed up to 5 T field. In the magnetic field up to 2 T high-pressure synthesized MgB 2 (with 10 % of Ti) at 20 K behaves in the same manner as Nb 3 Sn at 4.2 K.In XRD patterns of magnesium diboride with the Ti added, we observed no evidence of titanium diboride or unreacted titanium and only one compound with titanium was identified, namely, titanium dihydride TiH 2 (or more strictly TiH 1.924 ). The sample with the highest critical current density and irreversible field in the temperature range of 25-10 K contained some amount of pure Mg that was rather homogeneously dispersed in the material.The critical currents and irreversible fields of magnesium diboride synthesized at high pressure with Ti added are higher than those in the case where Ta has been added.

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A systematic study of the structure and superconductive characteristics of high-pressure–high-temperature (2 GPa, 700–1000 °C)-synthesized and sintered MgB2 without additions from different initial powders was performed. Among various secondary phases Mg–B inclusions with a stoichiometry close to MgB12 were identified. With an increasing amount of these inclusions the critical current density increased. So these inclusions can be feasible pinning centres in MgB2. The highest jc values in zero field were 1300 kA cm−2 at 10 K, 780 kA cm−2 at 20 K and 62 kA cm−2 at 35 K and in 1 T field were 1200 kA cm−2 at 10 K, 515 kA cm−2 at 20 K and 0.1 kA cm−2 at 35 K for high-pressure-synthesized magnesium diboride and the field of irreversibility at 20 K reached 8 T. The average grain sizes calculated from x-ray examinations in materials having high jc were 15–37 nm.

Magnesium diboride superconducting wires and bulk samples synthesized at high pressure have been produced with a variety of reactive metal additions. All these samples showed high critical current densities, but here we are most interested in the striking result that reactive metal additions such as titanium 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 10 wt% of Ti. In bulk materials the Jc values can be increased by even larger values, and the irreversibility field at 20 K increased to above 7 T. In a detailed study of the microstructure of these materials we have shown that PIT ex situ wires with 10 wt% titanium additions have a complicated layered microstructure around the Ti-rich particles, possibly forming titanium–boron phases, but also incorporating impurity elements including hydrogen. X-ray diffraction data, TEM and elemental mapping in the NanoSIMS 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 are extremely beneficial in MgB2 wires and bulk materials because they preferentially adsorb deleterious impurities from the superconducting matrix.