The structural features of superconductors prepared under various conditions were analyzed by means of transmission electron microscopy. The MgB2 crystal was identified as having an hexagonal structure with the space group: P6/mmm. Superconducting materials synthesized under a pressure of 6GPa were made up of regularly stacked grains as large as a few μm in size. The stacking faults and microstructural properties of grain boundaries with or without impurities, which appeared in a sample with a critical current density greater than 105A/cm2, were systematically investigated.

Structural Properties of MgB2 Superconductors with a Critical Current Density Greater than 105A/cm2. J.Q.Li, L.Li, Y.Q.Zhou, Z.A.Ren, G.C.Che, Z.X.Zhao: Chinese Physics Letters, 2001, 18, 680-3