Comparison between nano-diamond and carbon nanotube doping effects on critical current density and flux pinning in MgB₂

Doping effects of nano-diamond and carbon nanotubes (CNTs) on critical current density of bulk MgB₂ have been studied. CNTs are found prone to be doped into the MgB₂ lattice whereas nano-diamond tends to form second-phase inclusions in the MgB₂ matrix, leading to a more significant improvement of J_c(H) by doping by nano-diamond than by CNTs in MgB₂. TEM reveals tightly packed MgB₂ nanograins (50–100 nm) with a dense distribution of diamond nanoparticles (10–20 nm) inside MgB₂ grains in nano-diamond-doped samples. Such a unique microstructure leads to a flux pinning behaviour different from that in CNTs-doped MgB₂.