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 650°C 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 J_C 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.