Effects of nano-carbon doping and sintering temperature on microstructure and properties of MgB2

We observed that NC was an effective dopant for MgB2 and that part of it was incorporated into the MgB2 while the other part remained (undoped), which reduced the grain size. The actual C content was estimated to be 68-90% of the nominal content. The NC doped samples exhibited lower Tc values and better Jc(B) behavior than the undoped samples. The doped sample sintered at 900 °C showed the highest Jc value due to its high doping level, small amount of second phase, and fine grains. On the other hand, the Jc was decreased at a sintering temperature of 1000 °C as a result of the formation of MgB4 phase.