The effect of carbon and rare earth oxide co-doping on the structural and superconducting properties of MgB2

Carbon (C) and rare earth oxide (REO) co-doped bulk polycrystalline MgB2 samples with nominal compositions Mg1-y(REO)(y)(B0.95C0.05)(2) (where y = 0.00, 0.01, 0.03, 0.05 and REO = Eu2O3 or Pr6O11) have been synthesized via a solid state reaction route. The XRD results reveal the presence of impurity phases EuB6 in Eu2O3 and PrB4 and PrB6 in Pr6O11 co-doped samples along with the main hexagonal phase of MgB2 and a small amount of MgO. The values of upper critical field (H-c2) and irreversibility field (H-irr), except H-c2 of y = 0.05 for Eu2O3, have been found to increase at all temperatures (6.5 T) region. At 20 K enhancement in the high field (>6 T) J(c) values for y = 0.01, 0.03 of Eu2O3 and y = 0.01 of Pr6O11 co-doped samples are also reported in the present work. The correlations between the structural characteristics and the observed superconducting properties of the co- doped samples are described and discussed in this paper.