The effect of citric and oxalic acid doping on the superconducting properties of MgB2

In this paper we report the effect of carbon doping on the structural and superconducting properties of MgB2 using citric and oxalic acids as carbon sources. The bulk polycrystalline samples have been synthesized via a standard solid state reaction route with composition MgB2 + x wt% of citric and oxalic acids (x = 0, 5 and 10). The x-ray diffraction results reveal the formation of dominantly MgB2 with only a small amount of impurity phase MgO and substitution of C at the B site of MgB2 for both dopants. Improvements in the upper critical field (H-C2), irreversibility field (H-irr) and high field (>2.5 T) critical current density (J(C)) have been observed on C doping in the samples. The correlations between superconducting properties and structural characteristics of the samples are described and discussed in this paper.