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 0.33Eu0.33Gd0.33)Ba2Cu 3Oy, superconductor. We found two types of stable nanometer-scale particles, small LRE-Ba2CuZrOy and (LRE-Zr)BaCuOy (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-Tc superconducting magnets.
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