HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY OF (1212) BI-CUPRATE SUPERCONDUCTOR MATERIALS

Powders as well as ion-thinned compressed powder specimens in the form of pellets are investigated by 300 keV high-resolution transmission electron microscopy and selected area electron diffraction techniques. They reveal, as the majority and superconducting phase, an oxide with the bulk composition Bi0.5Cu0.5Sr2y0.8Cu2.2O6.9, as previously determined. High-resolution electron micrographs are compared with contrast simulation, based on the dynamical theory of electron diffraction. This comparison reveals the position of the metal atoms within the unit cell. The lattice parameters of the tetragonal unit cell, consistent with previous X-ray measurements, are a = 3.75 +/- 0.08 angstrom and c= 11.53 +/- 0.2 angstrom, as measured in selected area electron diffraction patterns. The crystal structure deduced from the high-resolution micrographs corroborates the 1212-structure type suggested on the basis of X-ray powder data (Ehmann et al., 1992). The material is virtually free of planar defects.