Arnie. R. Moodenbaugh

Coexistence of, and Competition between, Superconductivity and Charge-Stripe Order in La{sub 1.6-{ital x}}Nd{sub 0.4}Sr{sub {ital x}}CuO{sub 4}

Previously we have presented evidence for stripe order of holes and spins in La{sub 1.6-x}Nd{sub 0.4}Sr{sub x}CuO{sub 4} with x=0.12. Here we show, via neutron diffraction measurements of magnetic scattering, that similar order occurs in crystals with x=0.15 and 0.20. Zero-field-cooled magnetization measurements show that all three compositions are also superconducting, with the superconducting transition temperature increasing as the low-temperature staggered magnetization decreases.These results directly demonstrate an intimate connection between stripe correlations and superconductivity. {copyright} {ital 1997} {ital The American Physical Society}

Substitutions for Cu in YBa2(Cu1−xMx)3O7−δ (M = Fe, Co, Al, Cr, Ni, and Zn)

Abstract Substitutions for copper in YBa 2 (Cu 1− x M x ) 3 O 7− δ (1:2:3) were investigated. It was found that indirect methods to determine solubility into 1:2:3 typically used in the study of intermetallic compounds (observed variation with composition of superconducting transition temperature and of lattice parameters) are not entirely reliable. Optical micrography was used to asses the morphology of the sintered polycrystalline specimens. Differential thermal analysis provides melting point data signaling the presence of impurities which melt at lower temperatures. Electron microprobe studies were undertaken to determine actual M content of the superconducting phase and to check for the presence of impurity phases. Estimates of solubility limits are made. Transmission electron microscope studies were used to determine the twin structure and investigate the occurrence of a tweed pattern. Superconducting transition temperature as a function of x was determined below the solubility limits. In several cases T c s observed in this work differ from some previous reports. Possible sources of these discrepancies are discussed. Variation of lattice parameters as a function of x is reported. Also described are electrical resistivity and DC susceptibility measurements for selected samples.

Superconductivity in H/sub x/YBa/sub 2/Cu/sub 3/O/sub 7/

The preparation of H/sub x/YBa/sub 2/Cu/sub 3/O/sub 7/ by the direct reaction with hydrogen gas is described. The expansion of the original orthorhombic unit cell, as determined by x-ray diffraction, indicates that the system forms a hydrogen solid solution up to x--0.2; at higher H contents a hydrogen-rich phase is precipitated. The solid-solution phase exhibits a superconducting transition at --94 K, which was usually slightly higher than the original oxide. The H-rich phase(s), are not superconducting at 4 K or above. The maximum H content so far achieved corresponds to x = 5.9. The H-rich phases are stable at room temperature, at elevated temperatures (>473 K) they will decompose slowly under vacuum to form water and various solid products. They also slowly react upon exposure to room air.

Magnetoresistance in La1-xSrxCoO3 for 0.05 <~ x <~ 0.25.

The dc resistivity, magnetoresistance, and magnetic susceptibility of

FIELD-INDUCED STAGGERED MAGNETIC ORDER IN LA2NIO4.133

{\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}

Compressibility of the high-T/sub c/ superconductor La/sub 1. 7/Ba/sub 0. 3/CuO/sub 4/. sqrt. /sub y/

{\mathrm{Sr}}_{\mathit{x}}

Nuclear magnetic resonance study of polycrystalline Sr1-xCaxRuO3 (0le xle1.0)

{\mathrm{CoO}}_{3}

Dopant structural distortions in high-temperature superconductors: an active or a passive role?

compounds have been investigated in the temperature range of 4\char21{}300 K for magnetic fields up to 7 T. In the doping range studied (0.05\ensuremath{\le}x\ensuremath{\le}0.25) the electronic properties of the material exhibit a crossover from semiconducting to metallic behavior. The magnetoresistance is highest in the semiconducting state. A correlation was found between the energy gap determined from the dc conductivity and the energy scale identified from neutron scattering data. The results are interpreted in terms of a double-exchange model. \textcopyright{} 1996 The American Physical Society.