Jointing of Coated Conductors by Using Nano-particle Metal Pastes

Abstract Development of a jointing technique of coated conductors is important for all applications, such as superconducting magnets, cables, etc. Low resistance jointing techniques by means of silver diffusion [1] and for superconducting joints [2] have been reported so far. Since these processes were carried out at higher temperatures than the O 2 annealing temperature for appropriate carrier doping to the REBa 2 Cu 3 O 7-d (REBCO) crystals and resulted in oxygen deficiency in the REBCO crystals, long time O 2 annealing was required for compensation of this oxygen deficiency. Because the long time and high temperature post annealing is an inappropriate process as on-site technology, solder jointing technology has been widely accepted, in general, for practical applications. However, the resistance of the solder joint is 50 - 100 nΩ, and then the Joule heat generation in the joint region is a serious problem and must be solved. Consequently, we have studied a new jointing technique by using the pastes containing of silver or gold nano-particles. Because the I c value of GdBCO was deteriorated with higher temperature heat treatment, we have tried to develop a jointing technology with the low temperature (below 200°C). We used the nano-particle metal pastes (∼5 nm) which contained dispersants around the chemically active surface of nano-particles and dissociates at low temperatures and achieved the low resistance joint (∼ 3nΩ, 10 x 160 mm 2 , 77 K) as well as no I c degradation without O 2 post annealing.