Bulk samples of MgB2 doped with 0, 1, 3, and 5 wt% Pr6O11 nanopowder were prepared using a solid‐state reaction route. The lattice constants of Pr6O11‐doped MgB2 systematically increase with increasing doping level, indicating a partial substitution of Pr for Mg in the crystal structure, and consequently, the superconducting transition temperature, Tc, of MgB2 is slightly suppressed. At a low doping level of 1 wt% Pr6O11, the critical current density, Jc, and the irreversibility field, Hirr are improved. However, at higher doping levels, Pr6O11 doping seems harmful for the performance of MgB2 in high magnetic fields. It is argued that the effect of the doping mechanism of Pr6O11 on Tc and Jc is quite different from those of other rare‐earth elements, such as Y or Dy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon and titanium concurrently doped MgB 2 alloys with a composition of Mg 1−x Ti x B 2−y C y have been prepared by an in situ solid state reaction method. The combination effects of carbon and Ti doping on structure, microstructure, irreversibility field ͑H irr ͒, and critical current density ͑J c ͒ of MgB 2 have been investigated. It is found that doping Ti in MgB 2 does not reduce the solubility of carbon in MgB 2 , but, on the contrary, it eliminates the porosity present in the carbon-doped MgB 2 , resulting in an improved intergrain connectivity. As a result, J c and H irr of MgB 2 have been significantly improved, sharply contrasted to the situation of C-only-doped or Ti-only-doped MgB 2 bulks. Our results clearly reveal that carbon and Ti codoping are largely cooperative in improving the performance of MgB 2 in the high magnetic fields ͑Ͼ3 T͒ and at high temperature ͑ϳ20 K͒.

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