Two, differently processed, specimens were investigated by means of transmission electron microscopy. Both samples were found to be single-phase, with slightly different lattice parameters and different superconducting transitions. A specimen with a transition temperature of 95K was found to contain dislocations and lattice distortions that were due to cation disordering. The dislocations had Burgers vectors of the form, [100] and [110]; with an (001) glide plane. This was determined by using the g•b = 0 rule and 2-beam analyses. The other specimen had critical temperatures of 80 and 56K, and was found to contain a large number of almost periodically separated stacking faults on the (001) plane. The faults were due to CuO layers which were usually added to a single CuO layer, or sometimes removed from a double (CuO)2 layer. The stacking faults exhibited local superstructure-like ordering, with a repeat distance that varied with position in the specimen. The period was typically between 20 and 40nm. The extra ordered CuO layers appeared to be related to the double superconducting transitions.

Y.X.Guo, R.Høier, T.Graf, J.Y.Genoud: Philosophical Magazine B, 1995, 72[4], 383-90