FIZIKA A 9 (2000) 1 , 27-36

OPTIMISATION OF JOINTS BETWEEN SUPERCONDUCTING Bi₂Sr₂CaCu₂O_8+d AND Ag CURRENT LEADS

A. KURŠUMOVIĆ and J. E. EVETTS

IRC in Superconductivity and Department of Materials Science, University of Cambridge, Cambridge CB2 3QZ, UK.

Dedicated to Professor Boran Leontić on the occasion of his 70^th birthday

Received 14 February 2000; Accepted 10 April 2000

Electric contacts, for high current applications, between Bi₂Sr₂CaCu₂O_8+d superconductor and thick Ag tapes were in-situ processed during partial melting and texturing of the superconductor. At currents, I, below the critical current, I_C, a constant joint resistance, R_C, appears. Prolonged high-temperature annealing of current elements that produces samples of higher texture and higher I_C showed a correspondingly lower R_C hence lower power dissipation, due to lower contact resistivity (r_C » 55×10^-9 Wcm² at 77 K). Increasing the silver thickness further decreases power dissipation at joint. Current transfer occurs on a 1 mm scale in this regime. At higher currents (I > I_C), non-ohmic behaviour is observed. At very high currents (I » 10 I_C) the flux flow resistance of the superconducting element becomes comparable to the resistance of the Ag part in the joint, resulting in current sharing, approaching a rather uniform current distribution over the whole contact. This eventually reduces power dissipation in the contact to a value below that of the superconductor itself, reducing the possibility of element failure at the contact.

PACS numbers: 74.25.F, 81.40.R
UDC 538.945

Keywords: Bi₂Sr₂CaCu₂O_8+d superconductor, electric contacts, joint resistance, very high currents

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