Abstract:The process of cold seeding melt growth of GdBa₂Cu₃O_y (Gd123) bulk superconductors using NdBa₂Cu₃O_y (Nd123) thin films was reported. In addition, a novel cold seeding concept of combining MgO crystal and buffer pellet was also introduced. The misorientation caused by the lattice mismatch between MgO and Gd123 melt was overcome by choosing suitable heat treatment program and Gd₂BaCuO₅ (Gd211) content of the buffer pellet. The doping effect of soft ferromagnetic NiFe alloy particles was also reported. The bulk sample with 0.4% (mole fraction) doping amount shows the best performance on the flux trapping. The critical current density is largely enhanced under the external field of 1-2 T, which is promising for large-scale applications. This effect is originated from the substitution of Fe and Ni ions for the Cu sites contributing to magnetic flux pinning.

Key words: high temperature superconductor; crystal growth; cold seeding; chemical doping; magnetic flux pinning; critical current; second peak effect