Superconductivity Near 70K in a New Family of Layered Copper Oxides.

We have discovered a new family of layered copper oxide superconductors, with superconducting transitions near 70K. These materials are highly unusual because they can be synthesized only under slightly reducing conditions. We describe the synthesis crystal growth and crystal structure of various members of the family, and present measurements of basic physical properties. The unusual synthetic conditions open a whole new pathway to the discovery of new materials.