Effect of impurity additions on the microstructures and superconducting properties of in situ-processedMgB2 tapes

Abstract

We investigated the effect of various impurity additions forMgB2 tapesfabricated by the in situ process of the powder-in-tube method. As impurities, we tried silicides, suchas WSi2, ZrSi2, Mg2Si, SiO2 and SiC. These silicide powders were added to a powder mixture ofMgH2 and B. The content of the additives was changed from 2.5 to 20 at.%. The powdermixture was stuffed into an Fe tube of 6.2 mm outer diameter and cold-workedinto a tape with 0.5 mm thickness by the combination of grove rolling andflat rolling. Heat treatment was performed at a relatively low temperature of600 °C for 1 h under an argon gas atmosphere. An XRD observation of each tape indicated thatMg2Si was formed,except for the WSi2-added tape. The Tc of MgB2 decreased by all silicide additions. We obtainedJc enhancement for all of these additives, except forSiO2. The addition of SiCincreased Jc and decreasedthe field dependence of Jc. A high Jc value of2.5 × 104 A cm−2 at 4.2 K and 10 Twas obtained for the MgH2+B powder mixture and SiC addition. The irreversibility field of theMgB2 tape was enhanced from 17 to 22 T by the SiC addition. However, at low fields of T, the Jc enhancement by SiC addition seemed to be very small.