A series of monofilamentary powder-in-tube MgB2 wires were fabricated with 2 mol. C doping and co-additions of 0-3 wt. Dy2O3. Irreversibility fields (mu H-0(irr)), upper critical fields (mu(0)Hc(2)), and transport critical currents were measured, and from these quantities, anisotropies (gamma) and electronic diffusivities ( D-pi,D-sigma) were estimated. The addition of 1 wt. Dy2O3 to already optimally C-doped MgB2 wires produced higher H-c2//ab, H-c2//c, and Hirr values at 4.2 K. In addition, the critical current density, Jc, increased with Dy2O3 concentration up to 1 wt. where non-barrier Jc reached 4.35 x 10(4) A/cm(2) at 4.2 K, 10 T. At higher temperatures, for example, 20 K and 5 T, co-additions of 2 mol. C and 2 wt. Dy2O3 improved non-barrier Jc by 40 and 93 compared to 2 and 3 mol. C doping, respectively. On the other hand, measurements of T-c showed that C/Dy2O3 co-additions increase interband scattering rates at a lower rate than C doping does (assuming C doping levels giving similar levels of low-T mu 0Hc2 increase as co-addition). Comparisons to a two-band model for mu 0Hc(2) in MgB2 allowed us to conclude that the increases in H-c2//ab, H-c2//c, and H-irr (as well as concomitant increases in high-field Jc) with Dy2O3 addition are consistent with increases primarily in intraband scattering. This suggests C/Dy2O3 co-addition to be a more promising candidate for improving non-barrier J(c) of MgB2 at temperatures above 20 K.
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