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The important factors in obtaining a high-quality superconducting joint were investigated for the superconducting joint of a GdBa2Cu3Ox (GdBCO) bulk superconductor with sintered ErBa2Cu3Ox (ErBCO) using the local melt-growth method. REBCO (RE: rare earth) bulk superconductors can be used as strong magnets by magnetizing them, but they require large bulk sizes for their application. Although the superconducting joint presents a viable solution, many possibilities for property improvement remain, such as property degradation, depending on the joining direction. By varying the joining thermal conditions and confirming the elemental distribution, magnetization properties near the joined part and the effects of these on the joining properties are clarified, and a method for fabricating high-performance joined samples is obtained. Microstructure segregation was rarely observed at the center of the joined part regardless of the joining direction, and the superconducting properties were negligible and small. The Jc-B results are almost identical to those of the GdBCO matrix at a low field, confirming that the joined part minimally interferes with the superconducting current. Furthermore, by lowering the maximum temperature, shortening the holding time at the maximum temperature, and increasing the cooling rate, the region of mutual solid solution was reduced, and the Jc-B under the self-magnetic field was enhanced. These results contribute to the development of the superconducting joining method, a critical aspect of larger bulk superconductors.

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.

High-Temperature Superconductors (HTS) considerably accelerate the development of superconducting machines for electrical engineering applications such as fully electrical aircraft. This present contribution is an overview of different superconducting materials that can be used as magnetic screens for the inductor of high specific power electrical machines. The impact of the material properties, such as the critical temperature (Tc) and the critical current density (Jc), on the machine performances is evaluated. In addition, the relevance to flux modulation machines of different HTS bulk synthesis methods are addressed.

Pinning stability and the introduction of pinning centers are essential problems in the application of high temperature superconductors. A study of the role of the addition of a variety of oxides into Gd-123 bulk superconductors was pursued with respect to the effect of magnetic pinning centers on enhancement of critical current density. We have found the addition of magnetic alloy particles into Gd-123 bulk contributes to the enhancement of the critical current density under a magnetic field. The magnetic particles of Fe-B alloy with small amounts of Cu-Nb-Si-Cr were added into the Gd123 matrix and grown into single-domain bulk in air. The effects of Fe-B alloy magnetic particles on the superconducting pinning properties of Gd123 bulk are reported. The experimental results showed that the Tc of the bulk was suppressed significantly and the transition width became larger with an increase in the doping content of the magnetic particles. This was consistent with magnetic impurities suppressing superconductivity. The critical current density deduced from the magnetization as a function of applied external magnetic field was enhanced under low magnetic field and high magnetic field, which is different from the bulk doped with paramagnetic particles. Possible mechanisms and the role of magnetic materials from the viewpoint of increased flux pinning inside the bulk are discussed. [ABSTRACT FROM AUTHOR]

We employed Ba-Cu-O substrates for fabrication of bulk Y-Ba-Cu-O superconductors using the top-seeded melt-growth method. There were several advantages of using a Ba-Cu-O substrate as compared to conventional substrate materials such as MgO, ZrO2, Al2O3, RE123 (RE = rare earth) and RE211. The Ba-Cu-O substrate avoided crystallization from the substrate, suppressed liquid loss and scarcely reacted with the precursor. Furthermore, the introduction of large-sized cracks into a grown bulk was greatly suppressed by propagation along the interface between the grown bulk and the substrate. We were able to obtain bulk Y-Ba-Cu-O superconductors with uniform trapped magnetic field distributions and equal maximum trapped field values on both top and bottom surfaces, which indicates that the field-trapping capabilities were homogenized along the c-axes of the bulks fabricated on the Ba-Cu-O substrates. [ABSTRACT FROM AUTHOR]