Joining Y123 bulk superconductors using Yb–Ba–Cu–O and Er–Ba–Cu–O solders

We have succeeded in joining Y–Ba–Cu–O bulk superconductors using sintered Yb–Ba–Cu–O and Er–Ba–Cu–O bars as welding solders. The key to the fabrication of strongly coupled joints was the control of the welded surfaces such that both of the joined surfaces are parallel to the (110) plane. Another key was the use of highly dense sintered Yb–Ba–Cu–O and Er–Ba–Cu–O bars as welding solders. Microstructural observations have shown that welded regions were free from voids, residual liquid phase, and the segregation of second phase particles. The joint made with the Er–Ba–Cu–O solder was superior to that with Yb–Ba–Cu–O, presumably due to the inherently superior superconducting properties of Er–Ba–Cu–O.