Defect structure of superconducting YBa2Cu3O7−δ

Abstract
The superconducting material Y1Ba2Cu3O7−δ has been investigated by electron microscopy. Special attention has been paid to the defects occurring in the material. Twinning on (110) or (110) planes is intrinsically related to the orthorhombicity, and when cooled slowly the twin bands are pseudoperiodic with an average width of ˜ 50 nm. The orthorhombic‐tetragonal transition is reversible and diffusion controlled. Under particular conditions and in slightly reduced material a 2a0 X b0 superstructure resulting from vacancy ordering is formed. When kept in air under powder form the material seems to be unstable. Planar defects along (001) accompany the degeneration of the material.