Enhanced higher temperature irreversibility field and critical current density in MgB wires with DyO additions.

Bulk samples of magnesium diboride (MgB) doped with 0.5 wt% of the rare earth oxides (REOs) NdO and DyO (named B-ND and B-DY) prepared by standard powder processing, and wires of MgB doped with 0.5 wt% DyO (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 ( ), magnetic and resistive measurements of upper critical field ( ) and irreversibility field ( ), as well as magnetic and transport measurements of critical current densities versus applied field ( () and (), respectively). It was found that although the products of REO doping did not substitute into the MgB lattice, REO-based inclusions resided within grains and at grain boundaries. Curves of bulk pinning force density ( ) versus reduced field ( = / ) showed that flux pinning was by predominantly by grain boundaries, not point defects. At all temperatures the () of W-DY experienced enhancement by inclusion-induced grain boundary refinement but at higher temperatures () was still further increased by a DyO additive-induced increase in of about 1 T at all temperatures up to 20 K (and beyond). It is noted that DyO increases 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 conductors.