Effect of SiO 2 and SiC nano-powder doping was investigated for the powder-in-tube processed MgB 2 /Fe tapes. Mg or MgH 2 powder was used as the Mg source of starting materials, and heat treatment was carried out at 600 • C for 1 h. These heat treatment conditions of lower temperature and shorter heating time are advantageous from the aspect of practical production processes. MgH 2 powder improved the connection of MgB 2 grains and prevented oxidation of MgB 2 . SiC and SiO 2 doping greatly enhanced the critical current density (J C ) values of the tapes prepared with Mg + B powder. However, only the SiC doping was effective in enhancing J C values for MgH 2 + B powder. SiC doping decreased magnetic field sensitivity of J C , while SiO 2 doping did not change the field dependence of J C . The SiC doped tape showed transport J C value of about 6 500 A cm −2 at 4.2 K and in the magnetic field of 12 T. The irreversibility field increased from 17 T to 23 T by the SiC doping.

We measured the upper critical field, Bc2, of pure and SiC-added MgB2/Fe tapes prepared by the powder-in-tube process. We found that the Bc2 of the MgB2 tapes was much higher than the Bc2 of MgB2 single crystals. At 4.2 K, the Bc2 of the 10 mol % SiC-added MgB2 tape reached 22.5 T. This Bc2 was almost equal to the Bc2 of a conventional bronze-processed Nb3Sn conductor. At 20 K, the Bc2 of the 5 mol % SiC-added tape was around 10 T, which was comparable to the Bc2 of commercial Nb–Ti at 4.2 K. These results indicate that powder-in-tube-processed MgB2 tape is promising not only for high-field applications but also for applications at 20 K with a convenient cryo-cooler.

Fe-sheathed MgB2 tapes were prepared by the in situ powder-in-tube technique by 5 at% ZrSi2, ZrB2 and WSi2 doping, respectively. The doping effect of these compounds on the microstructure and superconducting properties of MgB2 tapes has been investigated by using x-ray diffraction, scanning electron microscope, transport measurements and dc susceptibility measurements. Compared to the undoped samples, Jc for all the doped samples were much improved; the best result in terms of Jc was achieved for ZrSi2 doping, by up to a factor of 3.4 at 4.2 K in magnetic fields up to 12 T. Moreover, these dopants did not significantly decrease the transition temperature. The Jc–B curves of WSi2-doped tapes show better performance in higher magnetic fields in comparison to undoped tapes, suggesting that pinning centres effective in a high-field region were possibly introduced.

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