X-RAY STUDY OF SUPERCONDUCTING SINGLE-CRYSTALS OF THE Y-PHASES

X-ray diffraction study of YBa2Cu3O7-delta a single crystals with inte rmediate oxygen content showed an ordered arrangement of oxygen atoms in the cuprate planes. Depending on the oxygen content, the blocks of the compositions YBa2Cu3O7 and YBa2Cu3O6.5 Or YBa2Cu3O6.5 are formed i n the crystals. It is shown that the so-called superconducting tetrago nal Y-phases are characterized by the presence of regions with the loc al orthorhombic symmetry. The tetragonal symmetry on their diffraction patterns is ''imitated'' by merohedral twinning.