Superconducting Characteristics of Polycrystalline Magnesium Diboride Ceramics Fabricated by a Spark Plasma Sintering Technique

Highly densified MgB 2 superconductors were successfully fabricated using a spark plasma sintering (SPS) technique, and their superconductivity with respect to microstructural evolution was evaluated. Full densification with final density close to the theoretical density was achieved at a temperature of 1000°C within a total SPS processing time of 40 min. Both an MgB 2 specimen sintered at 1000°C for 30 min and one sintered at 1050°C for 10 min exhibited a high critical transition temperature ( T c ) similar to that of an MgB 2 single crystal (39 K), and a very sharp superconducting transition width (Δ T ) less than 0.5 K. In addition, high critical current densities ( J c ) of 7.7 × 10 5 A/cm 2 in a field of 0.6 T at 5 K and of 8.3 × 10 4 A/cm 2 in a field of 0.09 T at 35 K were obtained. These excellent superconducting characteristics of the SPS‐processed MgB 2 are attributed to uniformly distributed secondary MgO phase nanoparticles and well‐developed dislocations in the microstructure that may act effectively as extrinsic flux pinning sites, resulting in the strong pinning force showing a high J c of 8.7 × 10 4 A/cm 2 even in the condition of a field of 4 T at 5 K.