Effect of nano-C doping on the in-situ processed MgB2 tapes
  The effect of nano-C doping on the microstructure and superconducting properties of Fe-sheathed MgB2 tapes prepared through the in-situ powder-in-tube method was studied. Heat treatment was performed at a low temperature of 650C for 1 h. Scanning electron microscopy investigation revealed that the smaller grain size of MgB2 in the samples with the C-doping. Further, the a-axis lattice parameter and transition temperature decreased monotonically with increasing doping level, which is due to the C substitution for B. High critical current density Jc values in magnetic fields were achieved in the doped samples because of the very fine-grained microstructure of the superconducting phase obtained with C doping. 
Xianping Zhang, Yanwei Ma*, Aixia Xu, Yulei Jiao, Ling Xiao, S. Awaji,   K. Watanabe, Huan Yang, Haihu Wen