COPPER-DEFICIENCY IN ND2-XCEXCUO4, GD2-XCEXCUO4 CRYSTALS AND OXYGEN DISORDER IN GD2CUO4 CRYSTALS

The structure of seven Nd2-xCexCuO4(x=0 and x=0.18) and Gd2CuO4 single crystals is determined by means of X-ray diffraction. All crystals have the Nd2CuO4 tetragonal T′ structure, space group I4/mmm (139). The copper site is found deficient (3-6%) in six crystals whereas both oxygen sites (within the CuO2 planes O(1) and between rare earth layers O(2) remain fully occupied within standard deviation. The vibration ellipsoids of Nd, Cu and O(2) appear to be more ellongated in the c direction in Nd-based crystals reannealed in an inert atmosphere than in as-grown ones. The oxygen of the CuO2 basal plane (O(1)) in Gd2CuO4 is found off-centered in the a direction by 0.18 (2) angstrom.