Low-temperature synthesis of MgB₂ superconductors

Abstract

MgB₂ superconductors have the outstanding potential to be integrated into diverse commercial applications. However, the critical current density J_c in MgB₂ is still smaller compared with expectations for an optimised material in these applications. Various flux pinning mechanisms are introduced into MgB₂ superconductors to improve J_c by different methods, including irradiation, chemical doping and ball milling. On the other hand, these methods mainly focused on the enhancement of pinning, but always neglect or even worsen the grain connectivity, which limits the further improvement in J_c. Recently, the low-temperature synthesised MgB₂ exhibits improved J_c due to the increases in both the grain connectivity and flux pinning. Ball milling pre-treatment of original powders, usage of different Mg-based precursors and the additions of different metal or alloys are employed to enhance the sintering efficiency of MgB₂ at low temperature. Among them, the minor metal or alloy additions are proved to be the most convenient, effective and inexpensive way in accelerating the fabrication of MgB₂ superconductors at low temperature. Combining the advantages of metal-activated sintering and carbon doping, it is also proposed that the low-cost MgB₂ superconductors with further improved J_c will be rapidly synthesised at low temperature with metal and carbon-based chemical co-doping.

Keywords:

• MgB₂ superconductors
• Low-temperature synthesis
• Critical current density
• Activated sintering
• Co-doping
• Review

The authors are grateful to the National Natural Science Foundation of China and Shanghai Baosteel Group Company (grant no. 50834011 and no. 51077099) and Programme for New Century Excellent Talents in University for grant and financial support. This work is also supported by Seed Foundation of Tianjin University. The authors also thank Professor David Cardwell (University of Cambridge, UK) for his kind help in editing the manuscript.