Improved superconducting properties of in-situ PIT-processed MgB2 tapes

We fabricated pure and SiC-added MgB₂/Fe composite tapes using a MgH₂ starting powder and applying heat treatments at 600-800°C. At 4.2 K, upper critical field (B_c2) of 27 T and 22.5 T were obtained for the SiC-added tapes. This B_c2 at 4.2 K is comparable to that of the bronze-processed Nb₃Sn. For both the pure and SiC-doped tapes, the critical temperature (T_c) values increased with increasing heat treatment temperature. The slope of the upper critical field vs. temperature (B_c2-T) curves, dB_c2/dT, of the pure MgB₂ tape decreased with increasing temperature, a change leading to the lower B_c2 at 4.2 K. Thus, the critical current density (J_c) of pure MgB₂ tapes in high magnetic fields at 4.2 K decreased with increasing heat treatment temperature. The dB_c2/dT of the SiC-added tape, on the other hand, is almost independent of heat treatment temperature. Thus, the J_c at 4.2 K of SiC-added tape is also independent of heat treatment temperature. In the high temperature region, due to the higher T_c values, the J_c of the tapes heat-treated at 800°C exhibit higher values than the tapes heat-treated at 600°C. At 20 K, B_c2 values of 9-10 T were obtained for the pure MgB₂ tape heat-treated at 600°C and the SiC doped tape heat-treated at 800°C. These B_c2 values at 20 K are comparable to that of commercial Nb-Ti at 4.2 K. The 5 at.% SiC-added tape heat-treated at 800°C shows J_c(MgB₂ core) values higher than 10⁴ A/cm² at 20 K in 5 T and at 30 K in 1 T. These J_c values are among the highest obtained for MgB₂ tapes.