Synthesis of Dense MgB(2) Superconductor via In Situ and Ex Situ Spark Plasma Sintering Method

In this study, high-density magnesium diboride (MgB(2)) 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 MgB(2) bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and J(c)-B using two methods, ex situ (sintering MgB(2) 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 MgB(4) and MgO were found to be effective in improving the J(c)-B characteristics. In the ex situ method, the degradation of MgB(2) due to pyrolysis was more severe at temperatures higher than 850 °C. The sample that underwent SPS treatment for a short time at 850 °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 °C. Microstructural characterization and flux pinning (f(P)) analysis revealed the possibility of refined MgO inclusions and MgB(4) 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.