Filamentary MgB2 Superconductors with Titanium Barriers
Ti diffusion barrier has been applied for several Cu stabilized MgB2 wires. Pure Ti is well formable metal allowing formation of thin barrier layers which are not reacting with MgB2. Instead of, Ti is able to purify MgB2 filaments by absorbing some impurities during the final heat treatment. Ti has comparable coefficient of thermal expansion with MgB2, which allows heat treatment at higher temperatures than for Nb barrier wires. Consequently, higher critical current densities can be obtained with Ti. Higher Ti resistivity offers a depressing of coupling currents in AC regime. One disadvantage of Ti is the inter-diffusion with copper during annealing and partial contamination of Cu stabilization. Benefits of Ti diffusion barrier have been utilized for the manufacture of fine-filamentary wires with minimal filament diameter of 10 μm. High critical current densities and high resistances to tensile stress and torsion stress at twisting have been demonstrated for these wires. AC loss measurements have shown reduced losses with decreased filament size and with shortened twist pitch.
KeywordsMgB2 Ti barrier Critical currents Stability AC losses
This work was supported by the Slovak Scientific Agency under the project APVV-0495-10 and grant agency VEGA 2/0121/12.