Keeping bulk magnesium diboride superconducting at higher current densities

In this regard, magnesium diboride (MgB₂), a high-temperature superconductor, has received much attention owing to its low cost, light weight, and easy fabricability. It is posited that MgB₂ has the potential to replace conventional niobium-based superconductors in practical engineering applications. However, bulk MgB₂ suffers from the long-standing problem of an insufficient critical current density (the current density above which it is no longer superconducting) at high magnetic fields. This, in turn, greatly limits its large-scale applications.

To address this issue, researchers have tried adding external elements in controlled quantities, a process known as "doping," during the synthesis of bulk MgB₂, with little to no success. As Prof. Muralidhar Miryala from Shibaura Institute of Technology (SIT), Japan states, "So far, researchers have tried improving the critical current density of bulk MgB₂ by doping with silicon carbide, other carbon sources, silver, transition metals etc. However, further improvement of the critical current density of MgB₂ is crucial for several industrial applications."

Not all hope is lost, however. Prof. Miryala's team managed to show that sintering MgB₂ at around 800°C for 3 hours in an argon environment can lead to a superior superconducting performance. This was linked to the formation of an optimum microstructure at such processing conditions, which was revealed to play a major role in the superconductivity of MgB₂.

In a recent study published first on July 7, 2022, in Advanced Engineering Materials, Prof. Miryala's team made another breakthrough. They found that combining optimum sintering conditions with controlled addition of nanometer-sized amorphous boron and dysprosium oxide (Dy₂O₃) enhanced the high-field critical current density (J_c) of MgB₂ as well as its self-field. The study included Prof. M.S. Ramachandra Rao of Indian Institute of Technology Madras (IITM), India, who provided support for the global project based learning (gPBL) program at IITM , and contributions from K. Kitamoto, A. Sai Srikanth, and M. Masato from SIT, D. Dhruba from IITM.

What was remarkable about Dy₂O₃ as a dopant was that it had almost no effect on the superconducting transition temperature of MgB₂ (which remained stable at around 38 K).

Additionally, Dy₂O₃ addition led to the formation of DyB₄ nanoparticles, enhancing further flux pinning at MgB₂ nano grain boundaries. Further, use of nano boron precursor helped to create MgB₂ nano grains with exceptional grain-boundary flux pinning. As a result, a superior critical current density was achieved.

Using amorphous nanoboron as the starting ingredient, the team quantified the precise amount of Dy₂O₃ that needed to be added to significantly improve J_c in bulk MgB₂ superconductors. By analyzing the structure and composition with techniques such as X-ray diffraction and Raman spectroscopy, and the superconducting properties of doped bulk MgB₂, they found the ideal Dy₂O₃ doping range to be 0.5-1.5%.

With these findings, the team is excited about the future prospects of MgB₂. "These results demonstrate the potential of Dy₂O₃ doping alongside nanoboron precursors in realizing bulk MgB₂ for practical superconducting applications," says Prof. Miryala. "Our research adds to the existing literature on ways to improve J_c and could pave the way for real-life bulk superconductors, which are a beacon for sustainable technologies."

Hopefully, we are now one step closer to practically realizable superconductors.