Electrical and Superconducting Properties in Lap Joints for YBCO Tapes

The joint process between tapes of coated conductors is a critical issue for most applications of high temperature superconductors (HTSs). In this work several lap joints using different techniques were prepared for three different types of commercially available YBCO-coated conductor tapes, with and without copper stabilizer or stainless steel reinforcement layers. Lap joints with effective lengths in the range of 3 to 20 cm were prepared using low melting point In-Sn and Sn-Pb alloys as soldering materials. The electrical resistance, the critical current, and the n-index of the joints were calculated from the electric field vs. current (E x I) characteristic curves under DC current tests and by further subjecting the same samples to tensile stresses. The results showed that the reinforced tape is the more robust tape for the joint-making process, whereas the copper-stabilized tape presented the lowest joint resistivity but with a relatively smaller mechanical strength against tensile stress.