Flux pinning and superconducting properties of bulk MgB2 with Nb2O5 addition

Magnesium diboride (MgB2) is a promising superconductor due to its ease of fabrication, tunability, low cost, and lightweight nature. Enhancing its critical current density (Jc) is crucial for practical applications. In this study, we investigated the effects of niobium diboride (NbB2) formation in MgB2by incorporating Nb2O5 into the sample composition. NbB2 was chosen due to its lattice parameter similarity to MgB2 and its ability to reducing the c-axis parameter. The samples were synthesized using a solid-state sintering process in an argon atmosphere, with a temperature plateau of 775 degrees C for 3 h. The compositions were 1 Mg + 2B + x(Nb2O5), with x ranging from 0 to 0.0125. X-ray diffraction analysis confirmed that Nb2O5 reacted with magnesium, forming MgO, niobium metal, and Nb1-xB2. The MgO content in the MgB2 samples increased from 19.93 wt% in the reference sample to 28.55 wt% in the MgB2(Nb2O5)0.0125 sample. Despite this, all samples, both doped and undoped exhibited a superconducting onset transition temperature of around 37.95 K. The critical current density, estimated using Bean's critical state model, showed a decrease from 242.35 to 159.07 kA/cm2 at 20 K in self-field as the dopant concentration increased. However, with minimal addition, as in MgB2(Nb2O5)0.0006, Jcreached 297.58 in a self-field at 20 K and improved under an external field of 2 Tat 20 K, increasing from 27.64 to 32.64 kA/cm2. The reduced performance at higher dopant levels is likely due to the increased MgO content, which may counteract the potential benefits of niobium addition.