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A comparative study of pure, SiC, and C doped MgB2 wires has revealed that the SiC doping allowed C substitution and MgB2 formation to take place simultaneously at low temperatures. C substitution enhances H_{c2}, while the defects, small grain size, and nanoinclusions induced by C incorporation and low-temperature processing are responsible for the improvement in J_{c}. The irreversibility field (H_{irr}) for the SiC doped sample reached the benchmarking value of 10 T at 20 K, exceeding that of NbTi at 4.2 K. This dual reaction model also enables us to predict desirable dopants for enhancing the performance properties of MgB2.

We report specific heat measurements at magnetic fields up to 20 T on the recently discovered superconductor SmFeAsO 0.85 F 0.15 . The B-T diagram of a polycrystalline SmFeAsO 0.85 F 0.15 sample with T c = 46 K was investigated. The temperature dependence of B c2 was extracted from the specific heat curves, the corresponding B c2 (T = 0) value derived from the Werthamer-Helfand-Hohenberg formula being 150 T. Based on magnetization measurements up to 9 T, a first estimation of the field dependence of the inductive critical current J c is given. Evidence for granularity is found. The presence of a peak effect is reported, suggesting a crossover in the vortex dynamics, in analogy to the behaviour observed in high T c cuprates.

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Cold high pressure densification was found to substantially enhance the critical current density of binary in situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase of Jc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T, Jc was found to be increased by 53%. The decrease of the electrical resistance for densified wires reflects an improved connectivity. The values of Birr at 4.2 and 20 K were enhanced up to 0.7 T for densified wires. After applying pressures up to 6.5 GPa at 300 K, the relative mass density dm of the unreacted (B+Mg) mixture inside the filament increased up to 96% of the theoretical density. This corresponds to a relative mass density df in the reacted MgB2 filaments of 73%. A quantitative correlation between filament mass density and critical current density was established.

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