Synthesis of Dense MgB2 Superconductor via In Situ and Ex Situ Spark Plasma Sintering Method

In this study, high-density magnesium diboride (MgB2) bulk superconductors were synthesized by spark plasma sintering (SPS) under pressure to improve the field dependence of the critical current density (J(c)-B) in MgB2 bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and J(c)-B using two methods, ex situ (sintering MgB2 synthesized powder) and in situ (reaction sintering of Mg and B powder), respectively. As a result, we found that higher density with suppressed particle growth and suppression of the formation of coarse particles of MgB4 and MgO were found to be effective in improving the J(c)-B characteristics. In the ex situ method, the degradation of MgB2 due to pyrolysis was more severe at temperatures higher than 850 degrees C. The sample that underwent SPS treatment for a short time at 850 degrees C showed higher density and less impurity phase in the bulk, which improved the J(c)-B properties. In addition, the in situ method showed very minimal impurity with a corresponding improvement in density and J(c)-B characteristics for the sample optimized at 750 degrees C. Microstructural characterization and flux pinning (f(P)) analysis revealed the possibility of refined MgO inclusions and MgB4 phase as new pinning centers, which greatly contributed to the J(c)-B properties. The contributions of the sintering conditions on f(P) for both synthesis methods were analyzed.