Abstract
In view of the recent attention focused on electron superconductivity, we have prepared and analyzed the crystalline structures of Ce substituted Ln 2− x Ce x CuO 4− y (Ln=Nd and Gd) compounds. X-ray powder diffraction analysis shows that the Ce ions have been succesfully doped into the Nd sites of the tetragonal Nd 2CuO 4 lattice and the maximum Ce solubility limit is x c = 0.20. Linear decreases in both the c lattice dimension and the unit cell volume, V, with increasing x up to the solubility limit indicate the smaller Ce 4+ ions, not the larger Ce 3+ ions are present. The tetragonal unit cell dimensions of the 21 K superconducting Nd 1.85Ce 0.15CuO 4− y compound refined from a high quality powder diffraction pattern with a figure of merit F 30=267.3 (0.003, 35) are: a = 3.9463 (1) A ̊ , c = 12.0809 (2) A ̊ and V = 188.14 (1) A ̊ . X-ray results also show that the maximum Ce solubility limit in Gd 2CuO 4 is significantly lower, with x c=0.15. Linear decreases in c and V with increasing x in Gd 2- x Ce x CuO 4− y have also been obtained indicating the presence of Ce 4+ ions. The unit cell dimensions of the semiconducting Gd 1.85Ce 0.15CuO 4− y compound are a = 3.9023 (1) A ̊ , c = 11.8310 (2) A ̊ and V = 180.16 (1) A ̊ 3 .
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