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 °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 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.

A high density CaKFe ₄ As ₄ bulk sample was successfully synthesized using a spark plasma sintering (SPS) technique. The density of the synthesized sample was 5.02 g cm ⁻³ , corresponding to 96.2% of the theoretical density of CaKFe ₄ As ₄ . Moreover, a reasonably high Vickers hardness of 1 GPa was measured. The electrical resistivity of the SPS bulk sample was as low as approximately 600 μ Ω cm at 300 K, which is smaller than that of the ordinary sintered polycrystalline sample by nearly one order of magnitude, and exhibited a sharp superconducting transition with the transition width (Δ T _c ) less than 2 K, indicating an improved grain connectivity. The critical current density of the SPS bulk sample calculated from the magnetization hysteresis loops (magnetic J _c ) reached 18 kA cm ⁻² at 4.2 K under 5 T, which is the highest among the iron-based superconductor polycrystalline samples reported thus far.

Superconducting foams of YBa₂Cu₃O_y (YBCO) are proposed as trapped field magnets or supermagnets. The foams with an open-porous structure are light-weight, mechanically strong and can be prepared in large sample sizes. The trapped field distributions were measured using a scanning Hall probe on various sides of an YBCO foam sample after field-cooling in a magnetic field of 0.5 T produced by a square Nd-Fe-B permanent magnet. The maximum trapped field (TF) measured is about 400 G (77 K) at the bottom of the sample. Several details of the TF distribution, the current flow and possible applicatons of such superconducting foam samples in space applications, e.g., as active elements in flux-pinning docking interfaces (FPDI) or as portable strong magnets to collect debris in space, are outlined.

The FeSe compound is the simplest high-temperature superconductor (HTSc) possible, and relatively cheap, not containing any rare-earth material. Although the transition temperature, T_c, is just below 10 K, the upper critical fields are comparable with other HTSc. Preparing FeSe using solid-state sintering yields samples exhibiting strong ferromagnetic hysteresis loops (MHLs), and the superconducting contribution is only visible after subtracting MHLs from above T_c. Due to the complicated phase diagram, the samples are a mixture of several phases, the superconducting β-FeSe, and the non-superconducting δ-FeSe and γ-FeSe. Furthermore, antiferromagnetic Fe₇Se₈ and ferromagnetic α-Fe may be contained, depending directly on the Se loss during the sintering process. Here, we show MHLs measured up to ±7 T and determine the magnetic characteristics, together with the amount of superconductivity determined from M(T) measurements. We also performed a thorough analysis of the microstructures in order to establish a relation between microstructure and the resulting sample properties.

Infiltration of an optimal amount of liquid (Ba₃Cu₅O₈ denoted further as “035”) for efficient peritectic growth is a primary requirement in the infiltration growth (IG) processing of high-quality REBa₂Cu₃O_7-δ products. Recently, we optimized the Dy content and the time-temperature schedules for top-seeded IG processing of (Gd,Dy)Ba₂Cu₃O_7–δ [(Gd,Dy)BCO] single grain superconductors. Aiming to fabricate larger sized (Gd,Dy)BCO (80 wt. % Gd₂BaCuO₅ and 20 wt. % of Dy₂BaCuO₅) single grain bulk superconductors, different liquid phase [LP = ErBa₂Cu₃O_7–δ (Er-123) and mixed with 035] sources were employed and the LP content was optimized by varying its mass. The increase in Er-123+035 mass assured an abundant amount of liquids for peritectic reaction. The Er-123+035 ratio of 1:1.4 was found to be optimum. The optimized liquid phase infiltration enabled an effective control of (Gd,Dy)₂BaCuO₅ (211) secondary phase size and content in final microstructures. Bulk single-grain (Gd,Dy)BCO superconductors were fabricated by the top-seeded IG process with an LP mass of 1 and 1.4 wt. %. A fully grown single grain bulk (Gd,Dy)BCO superconductor was attained. The sufficient LP infiltration resulted in a greatly improved critical current and trapped field performance. Scaling of bulk volume flux pinning force was studied with the aim of identifying flux pinning mechanisms effectively occurring in the material.