Crystal structures of YBa₂Cu₃O_x and LnBa₂Cu₃O_x (Ln = Ho and Dy)

Structure determinations of YBa₂Cu₃O_x and LnBa₂Cu₃O_x (Ln = Ho and Dy) are carried out by single crystal X-ray diffraction. The x values obtained in the present analyses are about 6.0, 6.0 and 6.25 for Y, Ho and Dy compounds, respectively and they have tetragonal structure with space group P4/mmm. The structures are perovskite-related ones with the c axis triplicated due to the ordering of Ba and Y or Ln. All oxygen atom sites around Y or Ln atoms in the c plane are vacant. Almost all oxygen atom sites in the layers which contain the Cu(1) sites (4/mmm) are also vacant. The present YBa₂Cu₃O₆ crystal is found to be a semiconductor, which indicates the importance of the oxygen number for the occurrence of superconductivity in Y-Ba-Cu-O and Ln-Ba-Cu-O systems.