Observation of record flux pinning in melt-textured NEG-123 superconductor doped by Nb, Mo, and Ti nanoparticles

Flux pinning in melt-processed (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y "NEG-123" + 35 mol% Gd₂BaCuO₅ "NEG-211" (70 nm in size) composite doped by TiO₃, MoO₃ and Nb₂O₅ achieved record values. The optimum values of all three dopands were found to be around 0.1 mol%. Transmission electron microscope (TEM) analysis found clouds of <10 nm sized particles in the NEG-123 matrix, shifting the pinning particle size distribution to significantly lower values. TEM by energy dispersive X-ray spectroscopy (EDX) analysis clarified that these nanoparticles contained a significant amount of Nb, Mo, and Ti. Appearance of nanometer-sized defects correlated with a significantly improved flux pining at low and medium magnetic fields, which was particularly significant at high temperatures. In the Nb-doped sample, a record J_c value of 925 kA/cm² at the secondary peak field (4.5 T) was achieved at 65 K, 640 kA/cm² at zero field at 77 K, and 100 kA/cm² at 90.2 K, the last value having been up to now considered as a good standard for REBa₂Cu₃O_y "RE-123" materials at 77 K. The greatly improved J_c-B performance in Nb/Mo/Ti doped samples can be easily translated to large-scale LRE-123 (LRE = light rare earths, Nd, Eu, Gd, Sm) blocks intended for real superconducting super-magnets applications.