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Instantaneous high temperature improved the low-temperature sintering efficiency of the un-doped MgB 2 superconductor, and the MgB 2 was rapidly synthesized at 600 °C for only 2 h. In addition to the refinement of MgO impurity particles, the sudden high temperature induced defects within the MgB 2 grains, e.g. twinning crystal, and the J c performance is therefore significantly enhanced, about 2.2 × 10 3 A·cm − 2 at 4 T for bulk sample. Differed from the two-dimensional nucleation growth mode of the MgB 2 grains in the high-temperature sintered un-doped sample, the low-temperature sintered MgB 2 grains accord with the dislocation growth mechanism, relying on the thermal-stress-triggered twinning crystal. [ABSTRACT FROM AUTHOR]

A significant enhancement of critical current density (J c) was obtained in MgB2 +3wt.% glycine samples with a large amount of MgO. The improvements in J c and in the irreversible magnetic field (H irr) are attributed to the pinning effects of high C-substitution level, nanoscale MgO, and to the even boundaries of small grains. This doping method overcomes the degradation of J c under a low field in previously reported SiC-doped samples. Moreover, the formation of MgO was demonstrated to be the result of the reactions between Mg, CO2 and O2. [ABSTRACT FROM AUTHOR]