Superlattice Modulation and Superconductivity in the Electron-Doped Nd2CuO4-Xfx and Nd2-Xcexcuo4 Systems

We have observed a periodic superlattice modulation in Nd2CuO4 and in the electron-doped Nd2CuO4-xFx and Nd2-xCex-CuO4 by electron diffraction and microscopy. The superlattice modulation characterized by a wave vector q=( 1 4 1 4,0) parallel to the Cu-O plane was found in both superconducting and non-superconducting samples, but most of the samples examined were not homogeneous with respect to the superlattice. The orthorhombic superlattice phase is found to exist in four possible variants with its c-axis parallel to the four equivalent [111] zone-axes in the underlying tetragonal lattice. Samples quenched from high temperature invariably showed no superlattice or superconductivity; bulk superconductivity and regions of superlattice were observed on annealing in the range 250-750°C. We believe that oxygen migration is responsible for this disproportionation into superlattice and nonsuperlattice regions

Superconductivity at 60 K in La2-XSrxCaCu2o6the Simplest Double-Layer Cuprate

STARTING with the pioneering work of Bednorz and Müller1, many copper-oxide-based superconductors with high transition temperatures (T c) have been discovered. All contain layers of copper-oxygen squares, pyramids or octahedra as their electronically active structural components2,3. One structure type, first reported for La2SrCu2O6 and La2CaCu2O6 (ref. 4), has stood as an enigma since the beginning of high-T c research. This crystal structure4-7 (Fig. 1) is the least complex of all the structures with the double layers of copper oxide pyramids common to the compounds with highest T c, yet despite considerable effort, both published8,9 and unpublished, it has not until now been made superconducting. Here we report the successful synthesis and preliminary physical characterization of superconducting (La, Sr)2CaCu2O6. The highest transition temperature observed is 60 K at the composition La1.6Sr0.4CaCu2O6. This is a uniquely simple double-layer superconductor, which, like its single-layer analogue (La, Sr)2CuO4, becomes superconducting through the introduction of carriers in an unambiguous manner-by straightforward atomic substitution without the intervention of charge reservoir layers with flexible valence states

Crystal Growth and Substitutional Chemistry of Pb2Sr2MCu3O8

We report the crystal growth and ceramic preparation of Pb2Sr2MCu3O8 phases containing a variety of lanthanoids and lanthanoid/alkaline-earth metal solid solutions. These recently discovered high-temperature superconductors add to our understanding of the chemical and structural features key to superconductivity in cuprates. The growth of millimeter-sized crystals from PbO-rich fluxes is described. Ceramic samples of the Pb2Sr2MCu3O8 phase are formed under low oxygen partial pressures for the majority of the lanthanoids. Systematic structural changes are observed as a function of lanthanoid size. The substitution of alkaline-earth metals on the lanthanoid site and the substitution of barium for strontium to form Pb2Ba2YCu3O8 are also described