A search for superconducting impurity phases in cubic Ba2GdRu1 − uCuuO6

It is widely believed that cuprate (CuO2) planes are the essential structural component of all high temperature superconductors. In contrast, Wu et al. and Chen et al. have published evidence for superconductivity in Cu-doped double pervoskites which consist of alternating layers of either SrO or BaO with YRu1 − uCuuO4. These structures have no cuprate planes, yet exhibit diamagnetism to temperatures as high as 84 K. Since the chemical components of these materials are common to the rutheno-cuprates, it is widely believed that impurity phases are responsible for the observed superconductivity. Impurity phase formation and decomposition in a homolog, Ba2GdRu1 − uCuuO6, is investigated. It is found that this phase is stable against separation into GdBa2Cu3O7 and Ba2GdRuO6. GdBa2Cu3O7 does not survive high temperature processing with Ba2GdRuO6.