Processing of high-performance (Gd, Y)-Ba-Cu-O bulk superconductors with fine RE211 pinning centers

We have investigated the superconducting properties of (Gd, Y)-Ba-Cu-O bulk superconductors fabricated from precursors of Gd123-Y211 in a reduced oxygen atmosphere. The employment of ball-milled ultra-fine Y211 powder as a precursor material was very effective in enhancing critical current density (J_c), since RE211 inclusions in the melt-textured samples could be drastically refined with decreasing the particle size of Y211 starting powder. The maximum J_c value reached an extremely high value of 380 kA/cm² at 77 K in self-field. However, size reduction of RE211 led to inhomogeneous distribution of RE211 inclusions. The trapped magnetic fields of Ag-added single-grain samples 25 mm and 33 mm in diameters were 1.5 T and 2.0 T at 77 K, respectively.