Research Progress of Electromagnetic Properties of MgB2 Induced by Carbon-Containing Materials Addition and Process Techniques

Abstract

For the high transition temperature (T c ) and low cost taking both raw materials and fabrication process into account, MgB 2 has been a competitive candidate to replace the conventional NiTi superconductor for high-temperature application in fault current limiters, transformers, motors, magnetic resonance imaging, adiabatic demagnetization refrigerators, generators, etc. The carbon-containing materials addition induced high critical current density (J c ) is reviewed based on their influences on the upper critical field (H c2 ), flux pinning force, and connectivity. The doping effects were compared in the overview focusing on SiC, organic dopants, and graphene-related dopants. SiC doping is featured for the high-field critical current density, which is caused by the increased H c2 attributed to the substitution of carbon on boron site and the strong flux pinning force offered by the nanosized secondary phases in the MgB 2 matrix. Organic dopants have the advantage over SiC dopant for their relatively homogeneous distribution in the MgB 2 matrix based on wet mixing of the organics and the raw boron powders. Low doping level of two-dimensional materials can improve the superconducting properties in all measured fields because of the combined advantages of carbon substitution effect and grain connectivity. MgB 2 fabricated with carbon-encapsulated boron also introduces strong flux pinning centers in MgB 2 , which show weak destruction of the connectivity of the MgB 2 grains as reflected by the low-magnetic-supercurrent behavior. High-pressure treatment and diffusion method can fabricate highdensity MgB 2 superconductors with better connectivity and increase the J c compared with the in situ and ex situ methods. KeywordsCritical current density (J c ) • Flux pinning • Doping • 2D flux pinning centers * Chuanbing Cai

Various effects of aliphatic amino acids on the critical current of the MgB2 superconductor

“…This indicates that the amino acids have induced some disorder especially in the a-b plane of the structure and much less along the c-axis direction. A similar behavior of the lattice parameters is generally observed when MgB2 is formed in the presence of organic additives [49][50][51][52][53][54][55] and this is attributed to the substitution of carbon atoms on boron sites in the lattice. A decrease of the a-axis lattice parameter has also been detected in studies of Mg-deficient MgB2 [56][57][58].…”

Improving the superconducting properties of 100 m class MgB2 wire with 18+1 filaments produced via an internal Mg diffusion process

“…In conclusion, the diffusion distance of liquid Mg increased obviously, and more B powder could make contact with liquid phase, resulting in thicker MgB 2 layers. Moreover, it is concluded that the C coating is a credible carbon source that can acquire a more homogeneous doping effect because the C agglomeration impact is diminished [44].…”