STRUCTURE-ANALYSIS OF OXYGEN-DEFICIENT TLSR2CUOY BY NEUTRON-DIFFRACTION AND HIGH-RESOLUTION ELECTRON-MICROSCOPY

The crystal structure of orthorhombic TlSr2CuOy was determined by Rietveld analysis of neutron powder diffraction data with the aid of electron diffraction and high-resolution electron microscopy. We found that oxygen vacancies are formed along the a-direction in a CuO2-z sheet, which is consistent with a superstructure of twice the subcell along the b-direction. CuO6 octahedra and CuO4 square planes alternate along the b-direction by sharing their comers in accordance with the ordered oxygen vacancies in the CuO2-z sheet. An apical oxygen atom in the CuO6 octahedron is nearer to a TlO layer than an oxygen atom shared by a TlO6 octahedron and the CuO4 plane. A crystal-structure image obtained by high-resolution electron microscopy could be successfully reproduced by computer simulation using structure parameters obtained by neutron powder diffraction.