Effect of impurity additions on the microstructures and superconducting properties ofin situ-processed MgB2tapes

We investigated the effect of various impurity additions for MgB 2 tapes fabricated by the in situ process of the powder-in-tube method. As impurities, we tried silicides, such as WSi 2 , ZrSi 2 , Mg 2 Si, SiO 2 and SiC. These silicide powders were added to a powder mixture of MgH 2 and B. The content of the additives was changed from 2.5 to 20 at.%. The powder mixture was stuffed into an Fe tube of 6.2 mm outer diameter and cold-worked into a tape with 0.5 mm thickness by the combination of grove rolling and flat rolling. Heat treatment was performed at a relatively low temperature of 600 °C for 1 h under an argon gas atmosphere. An XRD observation of each tape indicated that Mg 2 Si was formed, except for the WSi 2 -added tape. The T c of MgB 2 decreased by all silicide additions. We obtained J c enhancement for all of these additives, except for SiO 2 . The addition of SiC increased J c and decreased the field dependence of J c . A high J c value of 2.5 × 10 4 A cm −2 at 4.2 K and 10 T was obtained for the MgH 2 +B powder mixture and SiC addition. The irreversibility field of the MgB 2 tape was enhanced from 17 to 22 T by the SiC addition. However, at low fields of T, the J c enhancement by SiC addition seemed to be very small.