Microstructure and superconducting properties of powder-in-tube processed MgB 2 tapes

Abstract

We fabricated MgB 2 tapes using a powder-in-tube method without any heat treatment. Commercial MgB 2 powder was put into stainless steel, Cu–Ni and pure Cu tubes, and the powder/tube composites were cold worked into tapes. The packing density of the MgB 2 layers and J c increased with increasing the mechanical hardness of the tube. A very dense and hard MgB 2 layer was obtained in the stainless-steel sheathed tape, and a high J c of ∼4.5×10 5 A/cm 2 at 4.2 K and zero field was obtained by extrapolating the J c– B curves. Some c-axis grain alignment of the MgB 2 layer was obtained for the tape conductors. The degree of this grain alignment increased with increasing the hardness of the sheath material. This grain alignment brought about the anisotropy in J c with respect to the field direction. A large anisotropy factor of about 10 was obtained in a field of 7 T for the MgB 2/(SUS 316) tape.