CONVERGENT BEAM ELECTRON DIFFRACTION STUDY OF Bi-BASED HIGH TEMPERATURE SUPERCONDUCTING LAYERED COMPOUNDS

Cleaved specimens of layered compounds Bi 2 Sr 2( CaCuO 2)n CuO 6, n = 0, 1 and 2 phases have been studied by convergent beam electron diffraction. The identity and the symmetry of the phases have been determined from the higher order Laue zone (HOLZ) rings and the symmetry of their [001] patterns. In the case of Bi 2 Sr 2 CuO 6, the [001] axial periodicity corresponds to the component of the wave vector of the monoclinic modulation along the c axis. Widely different axial periodicities have been obtained. This is interpreted as the manifestation of the variation of the monoclinic modulation. The presence of basal stacking fault lowers the symmetry of the [001] pattern.