Superconducting MgB2 Tapes Prepared Using Mechanically Alloyed Nanocrystalline Precursor Powder

For the preparation of MgB₂ precursor powder the technique of mechanical alloying was applied. Tapes with Fe- and Cu/Nb-sheath have been prepared by the powder-in-tube method using these nanocrystalline precursor powders consisting of Mg, B and during the high energy milling reacted MgB₂. Differences in the quality of the boron powders used for the preparation of MgB₂ powders have a distinct influence on mi- crostructure and superconducting properties of bulk samples and tapes. The high density of grain boundaries acting as pinning centers enhances the critical current density J_c up to 10⁴ A/cm² at fields of about 5 T (20 K) and 10 T (4.2 K) in Fe-sheathed tapes. The effect of nanoparticle additions like SiC and WC on the mi- crostructure and critical currents of bulk samples and tapes is discussed.