Microstructures in High-Tc Bi-based Superconductors

Microstructures of high-Tc Bi-based superconductors in a disk form and a tape form sheathed by Ag are examined by SEM and TEM. The disk specimens were prepared by the sol-gel method and are compact with few cavities. Bi-2212 or Bi-2223 grains grow with short heating times leading to rapid increases in magnetization. However, magnetization drops with further heating due to the formation of 2201 areas in the 2212 matrix or 2212 areas in the 2223 matrix together with the amorphization within the matrix. In the tape specimens prepared by conventional powder processing methods, thin plate-like grains grow large with some cavities among them. The Jc increases together with the grain growth and then drops slowly as the amorphization of the grains occurs.