Where does carbon go when it is doped into magnesium diboride (MgB2) and why the superconducting properties are improved? In this work, malic acid-doped MgB2 was investigated and it was shown that carbon encapsulates boron powder, prevents agglomeration and as a result reduces void fraction as was confirmed by the first detailed X-ray tomogram analysis. It was also found that carbon induces a lot of stacking faults within MgB2 grains. The critical current density is now comparable to commercial niobium titanium (NbTi) wire and further improvements are expected.
- Jung Ho Kim
- Sangjun Oh
- Shi Xue Dou
