The synthesis of new phases related to YBCO by complete replacement of the chain copper sites

The extent to which new phases may be synthesized by the replacement of the chain Cu sites (Cu1) in the YBa/sub 2/Cu/sub 3/O/sub 7/ structure was examined. Several new phases have been prepared, and it is demonstrated that, for cations which preferentially substitute at this site, it becomes possible to prepare phases in which the Ba cations have been totally replaced by Sr, e.g. EuSr/sub 2/Cu/sub 2/NbO/sub 8/. All phases of this type are tetragonal, and, using Rietveld refinement techniques and powder X-ray diffraction data, it has been confirmed that the Nb occupies only the Cu1 position and adopts octahedral coordination in EuSr/sub 2/Cu/sub 2/NbO/sub 8/. Phases involving other substituting cations are also discussed. Superconductivity has not been observed in these phases.