Effects of metal powder addition on the structure and critical current of Ni-sheathed PIT MgB2 tapes

MgB₂ commercial powder was encased in a Ni tube and rolled into a monocore tape of about 5 mm in width and 0.3 mm in thickness. Different kinds of metal powder, i.e., In, Sn, Ag, Cu and Ni, were added to the MgB₂ core. Addition of the low melting point metal powder, e.g., In and Sn, has been found to enhance significantly the J_c value in MgB₂ tapes. Annealing at a low temperature yields further increase in the J_c of tapes with In and Sn addition. The enhancement in J_c by the In addition and the low temperature annealing reaches a factor of 6-7. The J_c of the tapes with 10vol% In addition, annealed at 200°C for 10 h is on the order of 10⁵ A/cm² at 4.2 K and 0.5 T. The TEM observation shows that In fills up the gaps among MgB₂ grains. The additional annealing produces better impregnation of In in the core. The improvement in grain linkage seems to be the probable origin for the enhancement in J_c by the In addition. The optimum amount of In addition to the MgB₂ core is likely 10-15vol%. Ag, Cu and Ni powder addition yields no apparent effect on J_c of PIT MgB₂ tapes.