Crystal Structure of Superconductor Ba₂YCu2.89O6.80

Crystal structure of Ba 2 YCu 2.89 O 6.80 sigle crystal was determined by the X-ray diffraction method at room temperature. The space group is Pmmm with lattice parameters a = 3.8699(8) Å, b = 3.8667(8) Å and c = 11.688(2) Å. A specific structure was found in the c-plane sandwiched between two barium layers. The Cu-O bond perpendicular to the plane 1.828(6) Å is shorter than the normal bond 1.95 Å. Within the plane oxygen atoms show an extremely large thermal vibration.