Superconducting properties of NaCl doped MgB2 bulks fabricated by hot pressed sintering

Abstract

MgB2 bulks with NaCl doping amount ranging from 0–30 at% have been prepared by hot pressed sintering process. With the increase of NaCl doping amount, the c axis lattice parameter of MgB2 monotonously increases, indicating the substitution of Mg atoms by larger Na atoms. Meanwhile, the intensity of diffraction peaks of both NaCl and impurity phase of MgO increases. More compact morphology was found in the NaCl doped MgB2 samples. The critical transition temperature (Tc) decreases from 38.2 K to 36.8 K with the increase of NaCl doping amount from 0 to 30 at%, and the corresponding transition width of Tc (ΔTc) increases from 0.5 K to 1.8 K. When the doping amount of NaCl is not exceeding 10 at%, the Jc value is about 106 A/cm2 at 4.2 K, 3 T, and 5 × 105 A/cm2 at 10 K, 3T. Jc performance of the 5 at% NaCl doped MgB2 sample (NC05) reaches 6.8 × 105 A/cm2 at 20 K, 2T, which improves approximately 20% compared to the pure one, attributing to the better grain connectivity of MgB2 and enhancement of flux pinning force by NaCl doping.