Enhanced flux pinning and superconducting properties of bulk MgB2 with Nb addition

Abstract

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 MgB2Nb0.0025 to MgB2Nb0.005. The samples were synthesized by solid-state sintering in an argon atmosphere. The heating protocol consisted of a linear temperature increase to 775 °C, over 8 h, followed by a 3-h dwell at that temperature, and then controlled cooling to room temperature over an additional 8 h. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) compositional analyses confirmed that MgB2 remained the dominant phase, although traces of residual metallic niobium were detected. Among the MgB2 samples prepared, the optimal composition MgB2Nb0.0035 exhibited a critical temperature (Tc) of 38.21 K. In comparison, the reference MgB2 sample without niobium showed a slightly lower Tc of 38.14 K under the same synthesis conditions. Niobium addition resulted in a significant enhancement in the critical current density (Jc), with the optimal sample reaching 461.69 kA/cm2 at 20 K in self-field, compared to 350.13 kA/cm2 for the reference sample. Further analysis of Jc at different temperatures revealed no anomalies above 10 K. The MgB2Nb0.0035 sample achieved a maximum Jc of 601.41 kA/cm2 under self-field and 57.26 kA/cm2 in an external magnetic field of 3 T. Scanning Electron Microscopy (SEM) showed that niobium interacted with unreacted boron to form Nb–B-rich particles. These findings highlight the advantages of using metallic niobium, as it prevents the use of niobium oxide and reduces the presence of magnesium oxide formation. As a result, the performance of the MgB2 material is significantly enhanced, which is crucial for industrial applications.