Synthesis and properties of new family of superconducting copper oxides based on GaO layers

We have discovered the first layered superconducting copper oxide with small, fixed oxidation state cations separating the conducting CuO2 planes. This material, GaSr2Y1-xCaxCu2O7, is similar to YBa2Cu3O7 with the square planar copper chains replaced by chains of edge-shared GaO4 tetrahedra. Thus, oxidation can occur only for the copper ion located in square pyramidal coordination in the CuO2 plane. The undoped parent compound, x=0, does not show magnetic order above 4K, probably due to the presence of the thick, ionic region separating the CuO2 planes. However, this ionic region does not suppress high Tc superconductivity (∼70K) for the doped compositions