Direct observation and analysis of nanoscale precipitates in (Sm,Eu,Gd)Ba₂Cu₃O_y

We employed atomic-resolution high-angle annular dark-field scanning transmission electron microscope to characterize the chemical composition and nature of the nanoparticles dispersed in melt-processed (Sm _0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_y, superconductor. We found two types of stable nanometer-scale particles, small LRE-Ba₂CuZrO_y and (LRE-Zr)BaCuO_y (LRE=Sm,Eu,Gd) ones, in the 10-60 nm range, and larger particles of Gd₂BaCuO₂ "Gd-211," around 100 nm in size. A substantial increase of critical current density was observed up to 90 K. Experimental data were interpreted in terms of additive pinning by "large" defects and a point-like disorder. The nanosized particles open a new horizon for production of bulk high-T_c superconducting magnets.