Structural effects of impurities in Ba₄Er₂Cu₇O(15-δ): Incorporation of Au and of Al

We discuss the substitutional doping of the cuprate superconductor Ba₄Er₂Cu₇O₁₅, Er247, by aluminum and by gold that leach from the crucibles used during crystal growth. The parent phase is a member of a series of compounds which are structurally related to the 91 K superconductor Ba₂ErCu₃O₇, Er123, but which have alternative chain structures separating the infinite two-dimensional copper oxide sheets. Crystals doped with either aluminum or gold were characterized by single crystal X-ray diffraction. Measurements of ac and dc magnetic susceptibilities and resistivities show that the crystals are superconducting. Both aluminum and gold atoms replace chain copper atoms. To accommodate the preferred coordination geometry for aluminum, extra oxygen is also incorporated into that structure. (C) 2000 Academic Press.