Enhanced higher temperature irreversibility field and critical current density in MgB 2 wires with Dy 2 O 3 additions.

Bulk samples of magnesium diboride (MgB ₂ ) doped with 0.5 wt% of the rare earth oxides (REOs) Nd ₂ O ₃ and Dy ₂ O ₃ (named B-ND and B-DY) prepared by standard powder processing, and wires of MgB ₂ doped with 0.5 wt% Dy ₂ O ₃ (named W-DY) prepared by a commercial powder-in-tube processing were studied. Investigations included x-ray diffractometry, scanning- and transmission electron microscopy, magnetic measurement of superconducting transition temperature ( T _c ), magnetic and resistive measurements of upper critical field ( B _c2 ) and irreversibility field ( B _irr ), as well as magnetic and transport measurements of critical current densities versus applied field ( J _cm ( B ) and J _c ( B ), respectively). It was found that although the products of REO doping did not substitute into the MgB ₂ lattice, REO-based inclusions resided within grains and at grain boundaries. Curves of bulk pinning force density ( F _p ) versus reduced field ( b = B / B _irr ) showed that flux pinning was by predominantly by grain boundaries, not point defects. At all temperatures the F _p ( b ) of W-DY experienced enhancement by inclusion-induced grain boundary refinement but at higher temperatures F _p ( b ) was still further increased by a Dy ₂ O ₃ additive-induced increase in B _irr of about 1 T at all temperatures up to 20 K (and beyond). It is noted that Dy ₂ O ₃ increases B _irr and that it does so, not just at 4 K, but in the higher temperature regime. This important property, shared by a number of REOs and other oxides promises to extend the applications range of MgB ₂ conductors.