Abstract
We fabricated MgB2 tapes by a powder-in-tube method. Reacted MgB2 powder (ex situ method) or Mg(MgH2)+B mixed powder (in situ method) were used as the starting powder. We used stainless steel, carbon steel, Cu-Ni, and Cu tubes for the ex situ method. Jc and the anisotropy in Jc with respect to the field orientation of ex situ-processed tape rapidly increased with increasing mechanical hardness of the tube. Annealing after cold rolling significantly enhanced the Jc values for the stainless steel and carbon steel tubes. For the in situ process, pure Fe tubes were used as a sheath material. The superconducting properties, such as Tc, Jc, and Birr, of in situ-processed tapes were sensitive to oxygen contamination during heat treatment. Heat treatment under a closed Ar gas atmosphere was effective in suppressing the oxidation of the tapes and enhancing the Jc values. The Jc value at 4.2 K of the in situ-processed tape was significantly enhanced by SiC doping. At 20 K, on the other hand, little Jc increase was observed due to the degradation of Tc by SiC doping. Typical Jc values of 108 A/m2 at 4.2 K in 12 T and 1.4 × 108 A/m2 at 20 K in 4 T were obtained for in situ-processed tapes heat-treated under a closed Ar gas atmosphere. Birr of in situ-processed tape was much higher than that of the as-rolled ex situ-processed tape.
