Superconducting MgB2

MgB2 is a BCS superconductor discovered in 2001. Its promising properties, such as the highTc(~39 K), simple structure (see left), low costs of raw materials (Mg and B) and fabrication, and the absence of weak-link across grain boundaries, make MgB2 a promising material for applications at above 20 K. However, to meet application requirements, the properties of MgB2, especially the irreversibility field H* and high-field Jc, have to be improved through microstructure modifications: chemical doping, introduction of precipitates, and atomic-scale control of defects. The small length scale of these modifications means that structure and chemistry characterizations using the TEM are required to better understand the correlation between MgB2’s superconducting properties and its microstructure.

Bulk MgB2

Applications of MgB2 are mostly likely to be in the form of tapes or wires created by bulk reaction of powders or sintering of pre-reacted powders. Improved H* and Jc from introduction of impurities such as carbon is also likely to be required.

Significant progress in creating MgB2 wires has already been made, with Hypertech Inc and Columbus Inc both reporting long lengths and results from test magnet coils. However, impurity phases and porosity limit the connectivity and thus current carrying cross section and Jc of most bulk MgB2.

We have extensively examined the microstructure and microchemistry of bulk samples prepared by Akiyoshi Matsumoto of NIMS in which nanoscale SiC particles were introduced into the precursor B and MgH2 powders before reaction. These samples have the highest Hc2 of any bulk MgB2.

Thin Film MgB2