ZnO doping effects in melt-textured (Nd_0.33Eu _0.39Gd_0.27)Ba₂Cu₃O_y grown from MgO seed

We successfully grew high-quality single-grain (Nd_0.33Eu _0.39Gd_0.27)Ba₂Cu₃O_y pellets using MgO seed crystals, provided a small quantity of ZnO was added. T_c (onset) continuously decreased with growing Zn content. An optimum for ZnO, compromising good superconducting and electromagnetic properties, was 0.035 mol%. With this ZnO content, T_c>92 K, a critical current density of 100 kA cm^-2 was achieved at 77 K and 3 T, and the irreversibility field was >7 T. Perfect facet lines up to the bottom of the sample with the c-axis reflection plane appeared after the melt growth, implying a high density of the material and practically no liquid loss. Very small difference in the trapped field distribution on the top and bottom surfaces confirmed a uniform crystallographic structure and the electromagnetic properties of the pellet.