Strong Enhancement of Critical Current Density in MgB2 Bulk and Ni-Sheathed Tapes With Very Small Dy2O3 Additions

A series of polycrystalline samples were prepared by in situ reaction of Dy₂O₃ (0.5-5.0 wt.%) with Mg + B. While the superconducting transition temperature, T_c remained largely unchanged, the intragrain distribution of nano precipitates of DyB₄ and MgO led to strong enhancement in critical current density, J_c at lower field below 4 T. The best sample (with only 0.5 wt.% Dy₂O₃ additions) had a J_c (1 T) of around a factor of 4 higher compared to the pure sample at 6 K and 20 K indicating improved connectivity and pinning. On the other hand, ex situ Ni-sheathed tapes fabricated from the Dy₂O₃ added powders exhibited critical current, I_c (4.2 K) superior to those made from pure MgB₂ powders at higher field above 3 T. The former also showed lower anisotropy in I_c with respect to field direction.