MgB2 bulk and tapes prepared by mechanical alloying: Influence of the boron precursor

The influence of three different boron powders with two different nominal qualities as starting material for the preparation of MgB2 tapes on microstructure and superconducting properties was investigated. For the preparation of MgB2 precursor powder, the technique of mechanical alloying was applied. The reactivity of the precursor powder is highest for B powder with higher nominal purity. The optimum annealing temperature for the formation of MgB2 phase in the tapes was found to vary because of the different reactivities of precursor boron powders. The jc of 5 x 104 A/cm2 (at 20 K, 3 T) for our tapes is higher than the jc of undoped samples prepared by the conventional in situ technique. Hence, the phase content, the density, and the superconducting properties of MgB2 tapes depend on the choice of the boron powder