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. 2021 Dec 2;14(23):7395.
doi: 10.3390/ma14237395.

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

Joseph Longji Dadiel  1 , Sugali Pavan Kumar Naik  2   3 , Paweł Pęczkowski  4 , Jun Sugiyama  1 , Hiraku Ogino  1   3 , Naomichi Sakai  1 , Yokoyama Kazuya  5 , Tymon Warski  6   7 , Anna Wojcik  8 , Tetsuo Oka  1 , Masato Murakami  1
Affiliations

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

Joseph Longji Dadiel et al. Materials (Basel). .

Abstract

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 (Jc-B) in MgB2 bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and Jc-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 Jc-B characteristics. In the ex situ method, the degradation of MgB2 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 Jc-B properties. In addition, the in situ method showed very minimal impurity with a corresponding improvement in density and Jc-B characteristics for the sample optimized at 750 °C. Microstructural characterization and flux pinning (fP) analysis revealed the possibility of refined MgO inclusions and MgB4 phase as new pinning centers, which greatly contributed to the Jc-B properties. The contributions of the sintering conditions on fP for both synthesis methods were analyzed.

Keywords: MgB2; critical current density; flux pinning; grain connectivity; microstructure; spark plasma sintering.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the research design, data collection, analyses, interpretation, writing the manuscript, or publishing the results.

Figures

Figure 1
Figure 1
Schematic diagram of an SPS furnace.
Figure 2
Figure 2
X-ray diffraction patterns for sintering temperature optimization of spark plasma sintered MgB2 bulk via the ex situ method.
Figure 3
Figure 3
The X-ray diffraction patterns for MgB2 ex situ further optimization at 850 °C.
Figure 4
Figure 4
Superconducting transition in the bulk MgB2 processed by SPS via ex situ (a) variation of the sintering temperature and (b) variation of the dwell time.
Figure 5
Figure 5
The magnetic field dependence of Jc curves determined at 20 K for MgB2 bulk superconductors fabricated by the SPS ex situ method for (a) sintering temperature variation and (b) dwell time variation.
Figure 6
Figure 6
X-ray diffraction patterns for spark plasma sintered MgB2 bulk via the in situ method.
Figure 7
Figure 7
The superconducting transitions in the MgB2 bulk synthesize by in situ process.
Figure 8
Figure 8
Shows the superconducting field performances of the Jc of the in situ process.
Figure 9
Figure 9
High magnification (30.000×) FE-SEM images for optimized fractured bulk samples produced by (a) SPS ex situ, (b) SPS in situ, and (c) polycrystalline MgB2. The subfigures (d–f) shows the statistical analysis of the grain size distributions.
Figure 10
Figure 10
TEM micrographs of optimized polished surfaces of (a) SPS ex situ and (b) SPS in situ.
Figure 11
Figure 11
The flux pinning diagram showing peak positions for the optimized in situ and ex situ samples compared with polycrystalline MgB2. There is a slight shift in peak positions to the right.
See this image and copyright information in PMC

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