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 (Jc) 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 Jc 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.