MICROSTRUCTURE OF SUPERCONDUCTING COPPER OXYCARBONATE THIN-FILMS OF THE BA-CA-CU-C-O SYSTEM

The microstructural state of a-axis-oriented superconducting oxycarbon ate films, grown by pulsed laser ablation, has been studied by high re solution electron microscopy (HREM). The member tn = 3 of the structur al family (CaCuO2)(m)(Ba2CuO2CO3)(n) is preferentially stabilized, in agreement with the nominal composition of the target, but m' members r anging between m' = 1 and 11 have been identified. Different types of domain boundaries, mainly parallel to {100}(p), or {110}(p), involve l ocal distortions of the framework. These non-stoichiometry features we re analysed, and were found to involve complex structural mechanisms s uch as variations of the cationic distribution within the different ty pes of layers, intergrowths perpendicular to the layers, and intercala tions of [CaCu2O3] and [Ca2CuO3]-type layers.