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

A comparative study of the electron transport properties of MgB₂ bulk samples was performed aimed at addressing the role of annealing as well as of SiC and Zn doping on sample anisotropy and band conduction parameters. Samples were produced by Reactive Mg Liquid Infiltration (RLI) technique in boron powder preforms. Both irreversibility (B _irr) and upper critical fields (B _c2) are enhanced by doping procedure. In all samples the B _c2 anisotropy factor (gamma), evaluated by analyzing the B _irr and B _c2 temperature dependence in the framework of the current percolation model proposed by Eisterer et al. [Phys. Rev. Lett. 90, 247002 (2003)], decreases at increasing temperature, and it is reduced by SiC and Zn doping-induced defects. Accordingly, in both annealed and doped samples the pi -band diffusivity, obtained by fitting the B _c2 dependence on temperature within the two-band model formulated by Gurevich [Phys. Rev. B 67, 184515 (2003)], is higher than the sigma-band one. A decrease of the more anisotropic sigma-band diffusivity was also found in the doped samples.