Synthesis of a high-T-c phase Nd1.85Ce0.15CuO4-y and its crystal-chemical features

To impart high-temperature superconductivity to a homogeneous phase with th e composition Nd1.85Ce0.15CuO4-y, equilibrium anneals were carried out unde r conditions that correspond to the low-oxygen boundary of the homogeneity region of this phase. Rietveld full-profile analysis in tandem with neutron diffraction was used to refine the structural parameters both for the obta ined high-T-c phase and for the phase with the same cationic composition af ter thermally processing it in various modes that could not induce high-tem perature superconductivity. A copper deficit was discovered in CuO2 layers, with the highest value of 11% observed in the sample annealed in air at 95 0 degreesC. A distinguishing feature of the high-T-c phase is the least dis tance between oxygen-deficient fluorite building blocks (Nd/Ce)(2)O2-y and almost oxygen-complete square CuO2 networks.