Keeping bulk magnesium diboride superconducting at higher current densities

Superconductors—wondrous materials whose resistance drop to zero below a critical temperature—show much promise to meet the growing energy demand of the global population. With potential applications in magnetic resonance imaging, nuclear magnetic resonance, magnetic drug delivery, fault current limiters, transportation (Maglev trains), and cables, there is much motivation for discovering and developing high-temperature superconductors.

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!

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Reference

DOI: https://doi.org/10.1002/adem.202200487

About Shibaura Institute of Technology (SIT), Japan

Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and will receive support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 8,000 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.

Website: https://www.shibaura-it.ac.jp/en/

About Professor Muralidhar Miryala from SIT, Japan

Dr. Muralidhar Miryala is a Professor at the College of Engineering/Graduate School of Science and Engineering and Board of Councilor at Shibaura Institute of Technology. His main area of research is Solid State Physics and Materials Science, with a special focus on materials for energy and environment, especially high-temperature superconductors. He has published over 500 research items, including patents, books, review-articles, articles, press releases, etc. He has received several awards for his research contributions, including the prestigious 2021 Pravasi Bharatiya Samman Award from the President of India and the SIT Excellent Education Award (2021) by Chairman of Board of Directors.

Funding Information

The study was supported by Japan Student Services Organization (JASSO) for the Global Project Based Learning (gPBL), Shibaura Institute of Technology (SIT) under the Top Global University Project, Designed by Ministry of Education, Culture, Sports, and Science & Technology in Japan. This study was partly supported by Shibaura Institute of Technology (SIT) International Research Center for Green Electronics, Grant-in-Aid FD research budget code: 721MA56383, and program Strategy AV 21-VP3 'Energy storage in flywheels.