Improved superconducting properties of in-situ PIT-processed MgB/sub 2/ tapes

We fabricated pure and SiC-added MgB/sub 2//Fe composite tapes using a MgH/sub 2/ starting powder and applying heat treatments at 600-800/spl deg/C. At 4.2 K, upper critical field (B/sub c2/) of 27 T and 22.5 T were obtained for the SiC-added tapes. This B/sub c2/ at 4.2 K is comparable to that of the bronze-processed Nb/sub 3/Sn. For both the pure and SiC-doped tapes, the critical temperature (T/sub c/) values increased with increasing heat treatment temperature. The slope of the upper critical field vs. temperature (B/sub c2/-T) curves, dB/sub c2//dT, of the pure MgB/sub 2/ tape decreased with increasing temperature, a change leading to the lower B/sub c2/ at 4.2 K. Thus, the critical current density (J/sub c/) of pure MgB/sub 2/ tapes in high magnetic fields at 4.2 K decreased with increasing heat treatment temperature. The dB/sub c2//dT of the SiC-added tape, on the other hand, is almost independent of heat treatment temperature. Thus, the J/sub 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/sub c/ values, the J/sub c/ of the tapes heat-treated at 800/spl deg/C exhibit higher values than the tapes heat-treated at 600/spl deg/C. At 20 K, B/sub c2/ values of 9-10 T were obtained for the pure MgB/sub 2/ tape heat-treated at 600/spl deg/C and the SiC doped tape heat-treated at 800/spl deg/C. These B/sub 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/spl deg/C shows J/sub c/(MgB/sub 2/ core) values higher than 10/sup 4/ A/cm/sup 2/ at 20 K in 5 T and at 30 K in 1 T. These J/sub c/ values are among the highest obtained for MgB/sub 2/ tapes.