A few atomic percent of 57Fe has been substituted for Cu in the YBa2Cu3O7−y system. Air-annealed samples are the superconducting 1-2-3 compound YBa2Cu3−x57FexO7−y while nitrogen-annealed samples are mainly the nonsuperconducting 2-1-1 compound Y2BaCu1−x57FexO5. X–ray, Meissner effect, and thermogravimetric measurements have been made on both compounds. The site dependence has been studied and compared in these two compounds by the Mössbauer effect with the result that Fe prefers the Cu(l) site in the 1-2-3 compound.

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