Influence of CNTs addition on structural and superconducting properties of mechanically alloyed MgB₂

The result of adding carbon nanotubes (CNTs) to the lattice parameters, critical temperature and electrical resistivity of the MgB2 superconductors is reported. Structurally, the addition of CNTs was found to decrease the a-lattice from 3.086 Å of CNTs free sample to 3.078 Å and 3.074 Å of 5% and 10% CNTs added samples due to a substitution of C at the B site which presence in the form of Mg(B1-xCx)2 main phase. The doping level x of CNTs added samples were 2.25 at% and 3.75 at% respectively. The unreacted CNTs presence as the second phase and further acting as the suppression agent for crystallite growth. The addition of CNTs is also to refine the grain size and improves the grain connectivity. Samples show a metallic behavior which observed only at temperatures above ~41 K, below which, a sharp transition of resistivity occurred toward zero resistivity, confirming the superconductivity behavior. This study concluded that the effect of CNTs addition affects the structural parameters and superconducting properties. The addition of the CNTs to 5% and 10% has changed the zero critical temperature of the sample material to respectively 39.20 and 38.02 K from 39.31 K of CNTs free sample.