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Journal ArticleDOI

Spectroscopic studies of atmospheric degradation of Y-Ba-Cu-O superconducting materials

15 Oct 1990-Journal of The Less Common Metals (Elsevier)-pp 1149-1156
TL;DR: In this paper, infrared reflectance spectroscopy was used to study the degradation of the ceramic superconducting oxides (YBa2Cu3O7 and YBa2cu4O8) under exposure to water vapour saturated air.
Abstract: Atmospheric degradation reactions of the ceramic superconducting oxides YBa2Cu3O7 and YBa2Cu4O8 and of (YBa2Cu3O7)1−xAgx (0 < x < 0.5) composites have been studied by infrared reflectance spectroscopy. Buildup of BaCO3 on the sample surfaces is accompanied by development of Reststrahlen features associated with internal modes of the carbonate ion. The rate of degradation of the YBa2Cu4O8 and the silver composites (YBa2Cu3O7)1−xAgx under exposure to water vapour saturated air is much lower than for YBa2Cu3O7 itself.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a photoemission technique was used to monitor surface degradation reactions in oxide superconductors, and the results showed that the extent of degradation is sensitively dependent on the chemical composition with metallic compositions being dramatically more unstable than nonmetallic compositions.

14 citations

Journal ArticleDOI
TL;DR: In this article, the effect of adsorption and intercalation of foreign molecules on the properties of high-temperature superconducting materials and on the reciprocal effect of superconductivity on the electronic state of adorbed molecules are considered.
Abstract: Data on the effect of adsorption and intercalation of foreign molecules on the properties of high-temperature superconducting materials and on the reciprocal effect of superconductivity on the electronic state of adsorbed molecules are considered. Particular attention is given to the analysis of experimental conditions and interpretation of the results obtained. An effect of adsorbed molecules on the electrophysical state and the critical parameters of superconductors is noted. Specific features of the interaction between the phases in the superconducting state and the external molecules are discussed. The bibliography includes 280 references.

10 citations

Journal ArticleDOI
M. Knupfer, G. Roth, J. Fink, J. Karpinski1, E. Kaldis1 
TL;DR: In this paper, the in-plane loss function between 0 and 50 eV and the plasmon dispersion of YBa 2 Cu 4 O 8 single crystals were investigated and the Fermi velocity and the effective mass of the charge carriers were derived.
Abstract: Electron energy-loss spectroscopy studies have been performed in order to investigate the in-plane loss function between 0 and 50 eV and the plasmon dispersion of YBa 2 Cu 4 O 8 single crystals. Strongly anisotropic dielectric functions and plasmon frequencies have been observed. The plasmon dispersion has been found to be quadratic, with an a-b anisotropy of about two. The Fermi velocity and the effective mass of the charge carriers could be derived.

9 citations

Journal ArticleDOI
17 Feb 2013
TL;DR: In this article, the physicomechanical, dynamic mechanical, superconducting, thermophysical, thermochemical and other properties of polymer nanocomposites were analyzed and the activated anionic polymerization of ǫ-caprolactam in the presence of various amounts of SiO2 nanoparticles.
Abstract: This paper analyzes available data on the synthesis and properties of polymer nanocomposites prepared by various techniques (sol-gel processing and microemulsion and frontal polymerizations) and containing polymethyl methacrylate, polydimethylsiloxane, natural rubber, and other polymers as binders, and various amounts of nano- and microadditives: SiO2, TiO2, FeO, clay, and Y1Ba2Cu3O7 − x . We consider the physicomechanical, dynamic mechanical, superconducting, thermophysical, thermochemical, and other properties of the polymer nanocomposites. Also examined are data on the activated anionic polymerization of ɛ-caprolactam in the presence of various amounts of SiO2 nanoparticles. Results on crystallization kinetics and electron microscopy data lead us to conclude that SiO2 nanoparticles act as heterogeneous nucleation centers for the crystallization of the forming poly(ɛ-caprolactam). Analysis of our results and data reported by other groups demonstrates that the intercalation of polymer macromolecules and their fragments into the interlayer spaces of ceramic grains increases the superconducting transition temperature of the ceramic by 1–3°C.

7 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that Ag substitutes Cu(1) in the lattice up to x = 0.12 and has an effect on the oxygen content and T c even at the low level of doping.

3 citations

References
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Journal ArticleDOI
J. Karpinski1, E. Kaldis1, E. Jilek1, S. Rusiecki1, B. Bucher1 
01 Dec 1988-Nature
TL;DR: In this paper, the authors reported synthesis of the superconducting phase YBa2Cu4O8 ('124') in bulk at 400 bar O2 and 1,040 °C.
Abstract: The superconducting phase YBa2Cu4O8 ('124') differs from YBa2Cu3O7 ('123') in having a double, instead of single, Cu–O chain running parallel to the b axis. It was first observed as a lattice defect in partly decomposed 123 powders1, and then as an ordered defect structure in inhomogeneous 123 thin films2,3, but has not up to now been synthesized in bulk. As part of a systematic study of the pressure–temperature–composition phase diagram of pseudo-binary Y–Ba–Cu–O systems at high oxygen pressure4,5, we have determined the approximate field of thermodynamic stability of the 124 phase. Here we report synthesis of the phase in bulk at 400 bar O2 and 1,040 °C. In agreement with previous measurements in thin films, the transition temperature is 81 K. Unlike the 123 compound, the oxygen content in 124 is thermally stable up to 850 °C, which may prove important for applications.

478 citations

Journal ArticleDOI
TL;DR: The superconductivity of YBa2Cu3O7 samples is greatly degraded by the interaction with water and humid air as discussed by the authors, which is probably due to the presence of nonequilibrium Cu3+ ions in this compound, but it should not preclude practical application of these materials since it should be possible to protect them with coatings of metal, glass, or plastic.
Abstract: We show that the superconducting YBa2Cu3O7 phase is highly sensitive to water and water vapor. This is probably due to the presence of nonequilibrium Cu3+ ions in this compound. In particular, the YBa2Cu3O7 phase decomposes in water to CuO, Ba(OH)2 and Y2BaCuO5 and evolves oxygen. Samples with a reduced oxygen content, e.g., YBa2Cu3O6.0, also decompose in an aqueous ambient. The superconductivity of YBa2Cu3O7 samples is greatly degraded by the interaction with water and humid air. This effect should not preclude practical application of these materials since it should be possible to protect them with coatings of metal, glass, or plastic.

352 citations

Journal ArticleDOI
01 Jul 1988-Nature
TL;DR: In this paper, a new Y-Ba-Cu-O superconducting oxide has been prepared as a distinct phase in thin films and the defect structure has a c-axis spacing of ∼27 A and a cation ratio of YBa2Cu4.
Abstract: Recently a new Y–Ba–Cu–O superconducting oxide has been prepared as a distinct phase in thin films1–3. The new phase was first seen as a defect structure in bulk samples of YBa2Cu3O7 (refs 4–7) and found to contain an additional copper layer7. The proposed defect structure has a c-axis spacing of ∼27 A and a cation ratio of YBa2Cu4. Y–Ba–Cu–O films containing a majority phase with a 27 A unit cell have been proposed as evidence of a distinct phase with the same structure as the defects (ref. 1 and K. Char et al., unpublished results). Films of the new phase superconduct with a transition temperature of 80 K (K. Char et al., unpublished results and refs 2 and 3). We show by X-ray crystallography of a film containing 85% of the new phase that the stoichiometry can be written as YBa2Cu4O8. The new structure differs from YBa2Cu3O7 in that the single, linear Cu–O chain parallel to the b-axis has been replaced by a double Cu–O chain with edge-sharing, square-planar oxygen coordination.

308 citations

Journal ArticleDOI
01 Sep 1989-Nature
TL;DR: In this paper, it was shown that substituting Ca for Y in Ba2Cu4O8 (124) increases Tc by ∼90 K and Y2Ba4Cu7O15 (247) achieves a superconducting transition of ∼ 90 K. But the lower Tc of 124 presents a major obstacle to practical uses of this phase at liquid nitrogen temperature (77 K).
Abstract: THE two superconducting phases YBa2Cu4O8 (124), containing double Cu–O chains, and Y2Ba4Cu7O15 (247), containing both single and double Cu–O chains, were originally discovered as lattice defects in the 90-K superconductor YBa2Cu3O7 (123)1. The synthesis of bulk superconducting 124 may be effected by a high-oxygen-pressure annealing technique2,3 and by reaction with ambient oxygen in the presence of alkali carbonates4. The oxygen stoichiometry of 124 is much more stable against high temperatures than that of 123 (ref. 2), a feature that is important for practical applications. But the lower Tc (80 K) of 124 presents a major obstacle to practical uses of this phase at liquid-nitrogen temperature (77 K). Here we report that partially substituting Ca for Y in 124 increases Tc. A superconducting transition of ∼90 K was achieved for the composition Y0.9 Ca0.1, Ba2Cu4O8.

263 citations

Journal ArticleDOI
01 Jan 1989-Nature
TL;DR: In this article, the authors reported the synthesis of the 124 phase in pure bulk form by a novel synthetic route in a flowing oxygen stream at 1 atm pressure, under oxidizing conditions.
Abstract: THE well-known 90-K superconductor Y2Ba2Cu3O7 ('123') is the first (n = 0) member of a homologous series of compounds with the general formula Y2Ba4Cu6+nO14+n. These compounds combine layers of copper–oxygen pyramids with single and/or double copper–oxygen chains. The n =2 member, Y2Ba2Cu7O8 ('124'), with double Cu–O chains, and the n = 1 ytterbium analogue, Yb2Ba4Cu7O15 ('247'), which mixes single and double chains, were first observed as intergrowths in bulk 123 by electron microscopy1,11. The 124 phase was then synthesized as a majority phase in thin films2,3,12, and its crystal structure was determined4 and found to be in agreement with the model proposed from microscopy. An important advance in the synthesis of bulk materials, the result of extensive pressure–temperature phase equilibria studies, was the isolation of 124 and 247 at oxygen pressures of >200 atm, and detailed determinations of their crystal structures (see, for example, refs 5–9). High-pressure studies have also shown that the 124 phase could be made with many rare-earth elements13. Here we report the synthesis of the 124 phase in pure bulk form by a novel synthetic route in a flowing oxygen stream at 1 atm pressure. This technique allows YBa2Cu4O8 to be synthesized without specialized equipment, will make it generally available for study of its normal and superconducting properties, and will make possible more extensive comparisons with YBa2Cu3O7 and other high-Tc superconductors. Our results suggest that 124 is the thermodynamically stable phase at low temperatures and 1 atm pressure, under oxidizing conditions; the usual inability to synthesize it in these conditions is probably due to the limitations of reaction kinetics.

228 citations