Crystal structure of the 80 K superconductor YBa2Cu4O8

A new Y-Ba-Cu-O superconducting oxide has recently been prepared as a distinct phase in thin films which superconduct with a transition temperature of 80 K. X-ray crystallography of a film containing 85 percent of the new phase is used to show that the stoichiometry can be written as YBa2Cu4O8. The new structure differs from YBa2Cu3O7 in that the single, linear Cu-O chain parallel to the b-axis has been replaced by a double Cu-O chain with edge-sharing, square-planar oxygen coordination. (C.D.)