Effects of Nanoparticle Doping on Electrical Properties of ${rm MgB}_{2}$ Bulks and Wires Obtained by Reactive Mg Liquid Infiltration Technique

摘要

The effect of SiC nanoparticle and colloidal C additions on the electric transport properties of ${rm MgB}_{2}$ samples, bulks and wires, was investigated at different applied magnetic fields. The samples were obtained by the Reactive Mg Liquid Infiltration (RLI) in boron powder preforms, technique with the advantages of good mechanical characteristics of the products with an easy manufacturing. It was found that SiC nanoparticle additions produce an improvement of both the irreversibility field and the upper critical field as well as the enhancement of the $n$-exponent in the power law voltage-current curves and of the pinning energy. In particular the analysis of the pinning energy dependence on the current density turned out that the SiC doping-induced pinning centers are of similar nature than the pristine ones. Moreover only a slight decrease of the critical temperature was measured as a consequence of the SiC doping. Higher pinning-capability enhancement was found for the C doped wires which exhibit a sharper irreversibility field enhancement at the external field increase. This issue together with a stronger critical temperature decrease (0.7 K) points towards a higher amount of C substitution for B in the ${rm MgB}_{2}$ lattice than in the SiC-doped bulk samples.