Atomic structure and chemistry of dense nano-precipitates in MgB2 ceramic

Ceramic MgB2 superconductor has great potential for applications in the devices. Doping MgB2 with carbon or SiC has been successful in improving critical current density Jc, the upper critical field Hc2 and flux-pinning. However, the presence of nano-precipitates, and their microstructure and chemistry, upon alloying/doping MgB2 grains are largely unexplored. In this paper, the atomic structure and chemistry of 5–10 nm dense nano-precipitates were discovered in purified MgB2 pellets by removing B2O3. The nano-precipitates are platelet-shaped and fully coherent with the MgB2 grains and having the longer axis of the plate perpendicular to the c-axis of MgB2 grains. Systematic conventional and analytical Transmission Electron Microscopy (TEM) was carried out to study the atomic structure and chemistry of those nano-precipitates. The practical experimental approach of optimizing the composition and synthesis heat treatment of MgB2 to induce dense uniformly distributed nano-precipitates is also discussed.