The effect of carbon and rare earth oxide co-doping on the structural and superconducting properties of MgB 2

Carbon (C) and rare earth oxide (REO) co-doped bulk polycrystalline MgB 2 samples with nominal compositions Mg 1 − y (REO) y (B 0.95 C 0.05 ) 2 (where y = 0.00, 0.01, 0.03, 0.05 and REO = Eu 2 O 3 or Pr 6 O 11 ) have been synthesized via a solid state reaction route. The XRD results reveal the presence of impurity phases EuB 6 in Eu 2 O 3 and PrB 4 and PrB 6 in Pr 6 O 11 co-doped samples along with the main hexagonal phase of MgB 2 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 Eu 2 O 3 , have been found to increase at all temperatures (< T c ) with increasing doping concentration of REO. Improvements in the values of critical current density ( J c ) at 10 K for y = 0.01 of Eu 2 O 3 and y = 0.01, 0.03 of Pr 6 O 11 co-doped samples have been observed in high fields (>6.5 T) region. At 20 K enhancement in the high field (>6 T) J c values for y = 0.01, 0.03 of Eu 2 O 3 and y = 0.01 of Pr 6 O 11 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.