Recently, a new copper oxide superconductor with an onset tem-perature of 28 K was found in the Nd-Ce-Sr-Cu-O system1. The superconducting phase was identified by X-ray diffraction and electron microscopy2, and the metal-atom positions are identical with those in the K2NiF4 or Nd2CuO4 structure, except for the order of the cations Nd(Ce) and Sr. Here we report the refinement of the crystal structure using neutron powder diffraction. We find that it comprises alternating slabs of the K2NiF4 and Nd2CuO4 structures, and that all the copper atoms are crystallographically identical, with oxygen in fivefold (square-pyramidal) coordination. In having only one kind of copper site, this new compound is structurally simpler than the other CuO5-bearing superconductors such as YBa2Cu3O7, and may therefore be particularly helpful in the effort to understand the origins of high-temperature superconductivity.
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