Preparation and enhancement of critical current density in MgB₂ wires and tapes

We have successfully prepared monofilamentary MgB₂ wires and tapes with different sheathed metals such as Cu, Ta/Cu and Fe by the powder-in-tube method. The phase composition, superconducting properties and microstructure features are investigated by x-ray diffractometer, the standard four-probe technique, SQUID magnetometer, SEM and TEM. The results indicate that J_c in MgB₂/Ta/Cu wires is higher than 10⁵ A cm^-2 at 5 K in 0.1 T and 10⁴ A cm^-2 at 20 K in 1 T. By Ti-doping, J_c can be significantly improved. MgB₂/Fe wires show very high transport critical current densities of 1.43 × 10⁵ A cm^-2 (4.2 K, 4 T), 3.72 × 10⁴ A cm^-2 (15 K, 4 T) and 2.34 × 10⁴ A cm^-2 (25 K, 3 T). Also the results indicated that small grain size should respond to the large J_c in Ti-doped MgB₂ tape and MgB₂/Fe wire.