YBCO/Ag boundary resistivity in YBCO tapes with metallic substrates

Abstract

The quality of the contact between a YBCO layer and the protective silver coating is an important parameter affecting the current transfer between YBCO and the normal metal. We studied experimentally the quality of this contact in 6 mm wide YBCO-coated conductor with a critical current of ∼60 A at 77 K. The measured current transfer length for the original sample of a YBCO-coated conductor covered by ∼3 µm thick silver and for the same sample additionally laminated by a 25 µm thin copper layer was 0.19 and 0.47 mm, respectively. The contact resistivity determined from these experiments was between 3.7 × 10−11 and 7.0 × 10−12 Ω m2. A direct measurement of the resistance between two overlapped tapes soldered by indium yielded values between 2.5 × 10−12 and 5 × 10−12 Ω m2. The boundary resistance and current transfer length are important parameters for the design of the optimal tape architecture for coils and windings, especially for stability issues.