High critical current density in Y-Ba-Cu-O bulk superconductors with very fine Y211 particles

We have succeeded in enhancing the critical current density (J_c) of melt-textured Y-Ba-Cu-O superconductors by employing ultra-fine Y211 powder as precursor. The Y211 starting powders were reduced down to 110 nm in diameter with ball-milling. Single-grain Y-Ba-Cu-O samples up to 33 mm in diameter were fabricated from the precursors containing finely milled Y211 powders. The Y211 inclusions in the melt-textured samples could be refined by decreasing the particle size of the Y211 starting powders. The maximum value of J_c at 77 K was 1.1 × 10⁵ A cm^-2 in a self-field. However, the size reduction of Y211 led to an inhomogeneous distribution of Y211 particles, in which the volume fraction of the Y211 phase greatly decreased near a seed crystal. An Ag-added bulk sample 33 mm in diameter exhibited a high trapped magnetic field of 1.6 T at 77 K.