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

Among the REBa2Cu3O7‐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 Sm2BaCuO5 (Sm211) particles has been challenging for high‐performance SmBCO bulks. Conventional precursor powders (SmBa2Cu3O7‐δ plus Sm2BaCuO5) intrinsically result in enlarging Sm2BaCuO5 particles due to their coarsening and epitaxial growth during the heating process. Here, we used modified precursor powders (MPPs, Sm2O3 plus Ba2Cu3O5) 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 Ba2Cu3O5 with Ba3Cu4O7) 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. [ABSTRACT FROM AUTHOR]