[WBP1] Conductor Processing & Evaluation

[WBP1-04] Flux Pinning and Superconducting Properties of Metallic Nb Added MgB₂

*Gaetan Simon¹ (1. Sibaura Institue of Technology (Japan))

Keywords:

MgB2,Nb addition,X-ray diffraction,Critical current density

Among known superconducting materials, MgB₂ stands out for its remarkably low density, offering new opportunities for lightweight, technologies across various industrial applications [1]. One promising direction is the development of high-power magnets for next-generation wind turbines. [2] MgB₂ is also an attractive candidate for hybrid and electric aircraft, where conventional propulsion systems are constrained by the heavy weight of engines, limiting both payload capacity, and economic viability.[3] Dihydrogen, with the highest specific heat capacity of all elements, is particularly suitable as a coolant in these systems. Moreover, it can serve a dual role as both coolant and fuel, thereby eliminating the need for onboard helium liquefaction systems, simplifying aircraft design, and enabling auxiliary thrust generation. Further, incorporating a third element into the MgB₂ matrix can lead to diverse effects such as elemental substitution, grain size modification, or the formation of secondary phases that act as vortex pinning centers, potentially enhancing flux pinning performance compared to pure MgB₂. In this study, we investigated the effects of niobium (Nb) addition on the superconducting properties of magnesium diboride (MgB₂). Niobium was introduced in varying amounts, with compositions ranging from MgB₂Nb_0.0025 to MgB₂Nb_0.0050. The samples were synthesized via solid-state sintering in an argon atmosphere. The heating protocol involved a linear temperature increase to 775 ^°C, over 8 hours, followed by a 3 hour dwell at that temperature, and then controlled cooling to room temperature over an additional 8 hours. [4] X-ray diffraction (XRD) and compositional analyses confirmed that MgB₂ remained the dominant phase, although traces of residual metallic niobium. Among the prepared samples, the optimal composition MgB₂Nb_0.0035 exhibited a critical temperature (T_c) of 38.14 K under the same synthesis conditions. Niobium addition led to a significant enhancement in the critical current density (J_c), with the optimal sample reaching 461.69 kA/cm² at 20 K in self-field, compared to 350.13 kA/cm²for the reference sample. Further analysis of J_c across different temperatures revealed no anomalies above 10 K. The optimal sample achieved a maximum J_c of 601.41 kA/cm² under self-field and 57.26 kA/cm² in a 3T external magnetic field. Scanning Electron Microscopy (SEM) showed that niobium interacted with unreacted boron to form Nb-B-rich particles. This was supported by XRD results, which indicated that approximately half of the added niobium remained in its metallic state, while the rest likely reacted with residual boron without forming niobium oxide. These findings highlight the advantages of using metallic niobium, as it prevents the formation of niobium oxide [5] and reduces the presence of magnesium oxide. As a result, the performance of the MgB₂ material is significantly enhanced, which is crucial for industrial applications.