Structural Properties of MgB₂ Superconductors with aCritical Current Density Greater than 10⁵A/cm²

Structural features of MgB₂ superconductors prepared under different conditions have been analysed by means of transmission electron microscopy. The MgB₂ crystal is identified to have a hexagonal structure with the space group of P6/mmm. Superconducting materials synthesized under a high pressure of 6 Gpa are made of regularly stacked grains as large as a few microns in sizes. Stacking faults and microstructure properties of grain boundaries either with or without impurities, appearing in a sample with the critical current density greater than 10⁵A/cm², have been systematically investigated.