STRUCTURAL COMPARISON OF ND2-XCEXCUO4-Y SINGLE-CRYSTALS AND POLYCRYSTALS

High-quality single crystals of Nd2-xCexCuO4 were prepared by a directional solidification technique for Ce concentrations x within the range 0<x<0.22 using CuO flux.The effect of post-growth annealing on the occurrence of a superstructure in these single crystals was studied using transmission electron microscopy. in contrast to reported polycrystalline ceramic samples prepared by a solid state reaction technique, superconducting as well as non-superconducting single crystal samples contained no evidence of superiattice regions even under different annealing conditions. The absence of the superstructure in both superconducting and non-superconducting samples clearlv indicates that superconductivity in the Nd-Ce-Cu-O system does not correlate to the superstructure.