Electron Microscopy of the Pb-Sr-Ca-Er-Cu-O Superconductor

The structure and microstructure of a solid state processed Pb-Sr-Ca-Er-Cu-O superconductor have been investigated by transmission electron microscopy. In addition to the majority superconducting phase, at least two other impurity phases have been observed. The superconducting phase is a layered structure similar to the Bi₂Sr₂CaCu₂O_y compound, with an extra Cu atom between the two PbO layers. Stacking defects inside the grain have been observed. A grain boundary amorphous phase has been observed. The steps in the resistivity-temperature plot and the absence of T_c,0 above 8 K are attributed to either the presence of the Pb₂Sr₂Cu₂O_y unit cell at the grain boundary and/or a local enrichment of oxygen at the grain boundaries. Superlattice spots in the [100] zone axis diffraction patterns from regions enriched in Ca and Er with respect to the nominal composition are due to ordering of Sr and Ca/Er in the Sr sites.