Improvement of critical current density in the Cu/MgB2 and Ag/MgB2 superconducting wires using the fast formation method

The powder in tube method has been used to fabricate Ag- and Cu-clad MgB2 wires using an in situ reaction method. The effects of short time sintering on the critical current densities of Ag- and Cu-clad MgB2 wires were studied. All the samples were examined using X-ray diffraction, scanning electron microscope, and magnetization measurements. For Ag-clad wire J(c) is improved by more than two times after the short time sintering process. J(c) values of 1.2 x 10(5) A/cm(2) in zero field and above 10(4) A/cm(2) in 2 T at 20 K have been achieved for Ag-clad MgB2 wire which is only sintered for a few minutes at 800 degreesC. However, a remarkable degree of reaction has been found between the superconducting cores and the sheath materials, leading to the formation of Cu2Mg and Ag3Mg for Cu- and Ag-clad wires, respectively. The results show that the short sintering causes less reaction between the magnesium and the sheath materials and markedly improves the critical current density. Our result shows that iron is still the best sheath material because of the lack of reaction between Fe and the superconducting MgB2 material. (C) 2002 Elsevier Science B.V. All rights reserved.