Recent progress in production of infiltration-growth and melt-growth processed bulk (RE)Ba₂Cu₃O_y

Novel methods are necessary to further increase the critical current density (J_c ) and uniformity of (RE)Ba₂Cu₃O_y (RE-123; RE - rare earth element) materials. In this contribution we address several issues of infiltration growth (IG) and melt-growth (MG) processing of RE-123 bulks and show recent progress: (i) optimization of 211 composition in IG-processed mixed YGd system type for the production of good-performance RE-123 bulks (RE: YGd), (ii) optimization of the thermal profile in IG processing of a mixed YEr-123 system for producing large bulks, and (iii) preparation of sharp-edge refined RE-211-phase particles by means of a high-energy ultra-sonication to improve performance of MG-processed Y-123. All products were studied by means of SQUID, SEM, TEM, and trapped field measurements at liquid nitrogen temperature. Our experimental results indicate that in an IG-processed mixed YGd-123 system, Y:Gd = 75:25 is the best ratio for optimum performance. In a YEr (Y:Er = 90:10) system, a series of isothermal experiments revealed that 990 C is the optimum temperature for maximum growth and performance. On the other hand, in the MG-processed bulk, the Y-211-phase particles exposed to ultra-sonic energy of 300 W for 80 min are smaller than those produced by a conventional process, mainly due to shearing and high-speed collisions of particles. As a result, a doubled-trapped field was achieved at 77 K as compared to traditional reference bulk. We will summarize the improved electromagnetic properties of IG- and MG-processed RE-123 bulks and their relation to microstructure changes in the final products.