A solid solution range exists between the systems YBa2Cu3O7-δ and (Pb,Cu)Sr2(Ca,Y)Cu2O7-δ has been successfully synthesized. The microstructures across the solid solution are complicated by the presence of an incommensurate or commensurate modulation. However, the studies indicate unambiguously that the structural modulation is neither a necessary nor sufficient condition for superconductivity among the composition across the solid solution. The modulation may be controlling the cation/oxygen positions in the charge reservoir layers, originating from the different oxygen positions in the perovskite-type (123-type) YBa2Cu3O7-δ and the rock salt-type (1212-type) (Pb,Cu)Sr2(Ca,Y)Cu2O7-δ. The discovery of the superlattice structures between YBa2Cu3O7-δ and (Pb,Cu)Sr2(Ca,Y)Cu2O7-δ adds yet a further chemical dimension to these systems, and may extend the possible avenues of research not only for superconductivity but also for structural chemistry.
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