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.