Behavior and effect of natural refinement of Sm₂BaCuO₅ derived from homogeneous nucleation catastrophe in bulks

Among the REBa 2 Cu 3 O 7‐δ (REBCO or RE123, RE = rare earth element) family, SmBCO is preferably used in top‐seeded melt‐growth (TSMG) because of its outstanding property and more controllable stoichiometry 123. Nevertheless, the refinement of Sm 2 BaCuO 5 (Sm211) particles has been challenging for high‐performance SmBCO bulks. Conventional precursor powders (SmBa 2 Cu 3 O 7‐δ plus Sm 2 BaCuO 5 ) intrinsically result in enlarging Sm 2 BaCuO 5 particles due to their coarsening and epitaxial growth during the heating process. Here, we used modified precursor powders (MPPs, Sm 2 O 3 plus Ba 2 Cu 3 O 5 ) in air‐processed TSMG, in which there is neither Sm211 in the beginning nor related enlargement during heating. Consequently, the nucleation catastrophe of Sm211 occurred above the peritectic temperature, which in situ formed, possessing naturally small size. Further, aiming to suppress the Sm/Ba substitution, Ba‐rich MPP, substituting Ba 2 Cu 3 O 5 with Ba 3 Cu 4 O 7 ) was employed, producing an excellent SmBCO bulk with a diameter of 24 mm: levitation force of 51.5 N and trapped field of 0.537 T. Optical micrographs and quantitative analyses confirmed the superior refinement and distribution of Sm211 particles in SmBCO bulks. Most importantly, new strategies in this work are widely applicable for developing cost‐effective and high‐performance other REBCO bulk superconductors.