Defect Structures and properties of MgB2 wires and bulks with O2 and Dy2O3 doping

MgB2 wires and bulks were fabricated via both reactive diffusion process of in-situ Mg+B powders processed above the melting temperature of Mg (bulks), and by gas-solid reaction of B+Mg vapor in an powder compact gas-diffusion couple (wires). SnO2 powder was added to the reactive diffusion route powders, and Dy2O3 powder was added to the B+Mg vapor route processed materials (in some cases to materials with underlying C-doping). Bc2 and Birr were measured resistively as a function of temperature up to 14 T. In both cases, the additions tended to increase the irreversibility field at moderate temperatures. The SnO2 decomposed and led to nanoscale MgO precipitates, the best BC2 for SnO2 doping is comparable to the best values (15 T at around 20 K) achieved by others in C-doped MgB2 bulks. In the case of Dy2O3, DyB4 precepitates were formed. TEM was used to quantify the preciptate sizes and distrubutions. It was seen that the additions tended to increase Birr but do not reduce Tc. Comparisons of C+Dy2O3 doping and C only doping showed that a larger Birr was acheivable with co-doping than by single element doping.