Magnesium diboride (MgB2) is one of the most promising superconductors, known for its ease of fabrication, tunability, low cost, and light weight. Enhancing its critical current density is essential for its practical applications. A recent study explored the effects of 54 different dopants on the superconducting transition temperature and critical current density of bulk MgB2 [1]. The study clarified that dopants and additives play a crucial role in improving the performance of bulk MgB2. In this research, we investigate the impact of combining niobium diboride (NbB2) with magnesium diboride, as NbB2 was selected due to its similar lattice parameter to MgB2 while reducing the c-axis parameter. Samples were prepared through a solid-state sintering process in an argon atmosphere, with a temperature plateau of 775°C for 3 hours. The compositions used were 1Mg + 2B + x(Nb2O5), with x ranging from 0 to 0.005. X-ray diffraction analysis confirmed that Nb2O5 reacted completely with magnesium to form MgO, along with niobium metal and Nb1-xB2. The MgO content in the MgB2 samples increased from 9.84 wt% in the reference sample to 15.02 wt% in the sample with MgB2(Nb2O5)0.005. Despite this, all samples, both with and without Nb2O5, exhibited a superconducting onset transition temperature of around 37.9 K. The critical current density (Jc), estimated using Bean's critical state model, showed a decrease from 267 to 255 kA/cm² at 20 K in a self-field as the dopant concentration increased. However, with minimal additon, such as in MgB2(Nb2O5)0.001, Jc remained stable in a self-field at 20 K and improved under an external field of 2 T at 20 K, increasing from 27 to 30 kA/cm². The reduced performance with higher dopant levels may be attributed to the increased MgO content, which could overshadow the benefits of niobium addition.
[1] Simon G and Muralidhar M (2024) Alloys and Compounds Communications, 100023.
Keywords: MgB2, Nb2O5 addition, X-ray diffraction, Critical current density