Identification of the Superconducting Phase in the Nd-Ce-Sr-Cu-O System

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Abstract
Phase search experiments were performed to identify the superconducting phase in the Nd-Ce-Sr-Cu-O system. A single phase superconductor was obtained form the nominal composition (Nd0.66Ce0.135Sr0.205)2CuO y . It has a tetragonal cell with a=3.8558(1) and c=12.487(1) Å. From powder X-ray diffraction and electron microscopic observations, it was confirmed that the metal positions in this phase are identical to those in the K2NiF4 structure but with cationic order of Nd(Ce) and Sr. Three structure models including oxygen positions are proposed and discussed. Although we could not be absolutely conclusive, the structure which consists of alternative stacking of K2NiF4- and Nd2CuO4-type slabs seems to be most likely.