DEFECTS AND FLUX CONTAMINATION IN ND2-XCEXCUO4, GD2-XCEXCUO4 CRYSTALS - OXYGEN DISORDER IN GD2CUO4 CRYSTALS

The structure of several Nd2-xCexCuO4 (x = 0 and x = 0.18) and Gd2CuO4 single crystals is investigated by means of X-ray and neutron diffraction. All crystals have the Nd2CuO4 tetragonal T' structure, space group 14/mmm. Single crystals for X-ray diffraction, prepared either by spontaneous crystallisation or growth from a flux (CuO), exhibit a significant copper deficiency. The oxygen of the CuO2 planes in Gd2CuO4 is found off-centered in the a direction. Larger Nd2CuO4 crystals, suitable for neutron diffraction, were produced with a higher amount of CuO in excess. In most of them, inclusions of Cu2O having their [110] or [111] direction perfectly aligned along the c-axis of Nd2CuO4 were detected. Structural refinement of a Cu2O free single crystal indicates a full occupancy of the Cu site but vacancies on both oxygen sites. © 1990.