Synthesis of MgB 2 superconductor under carbon induced virtual inert atmosphere

Abstract

A synthesis route for MgB 2 samples under carbon induced virtual inert atmosphere is explored to overcome the difficulties in preparing the samples under ambient environment, wherein carbon was used as a buffer to suppress the oxidation of Mg and to assist the formation of MgB 2. The buffering action of carbon was understood with the help of differential thermal and thermogravimetric analysis, carried out on both carbon powder and bulk blend of unreacted magnesium and boron. The magnesium content was systematically varied in different ratios with boron to get the optimum MgB 2 phase formation. The XRD studies revealed complete disappearance of unreacted B as well as Mg deficient phase of MgB 4 and the formation of MgB 2 for the B:Mg ratio of 1:1.5. The SEM studies for this ratio indicate, well developed grain growth due to the formation of optimum nucleation centers with increased Mg content. The superconducting transition for optimized sample was observed at 33.5 K by four-probe resistivity technique. The amount of carbon doped into the sample was determined from a well known method by analyzing the change in the in-plane lattice parameter. The susceptibility studies of sample showed Wohlleben effect in field cooled plot confirming the superconductivity in the sample.