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Abstract  

The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. The thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. The effects of substitution of Pb for Bi on the temperatures of formation of the superconducting phases is also discussed. STA has also been carried out under varying oxygen partial pressures to determine the effects of oxygen pressure on the formation and decomposition of the phases involved in the production of the 2223 compound.

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Abstract  

In this paper the theoretical approach and applications of Cahn ultramicrobalance to kinetic study on the thermal decomposition of the high-temperature Y1Ba2Cu3O7-x superconductor are presented. Thermogravimetric in situ measurements of oxygen loss from Y1Ba2Cu3O6 samples heated isothermally in a relatively high dynamic vacuum were performed with a Cahn RG electrobalance. Single-phase orthorhombic samples of composition Y1Ba2Cu3O7-x (highest oxygen content) were synthesized from stoichiometric (1:2:3) mixtures of high-purity Y2O3, BaCO3 and CuO. The original 1:2:3 mixture was prepared by the two-stage procedure described earlier. The crystal structure of the sample in the original orthorhombic phase was controlled by the X-ray powder method (CuKα radiation) using a Stadi P Stoe diffractometer with a position-sensitive detector. Activation energy is estimated from appropriate Arrhenius plots.

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Abstract  

We studied the chemical compatibility of Ag, Ag(In)alloy, Y2BaCuO5 (the so-called Y-211 green phase) and YBa2Cu3O7–δ (Y-123) phase in order to check if better grain growth and alignment with minimum contamination were possible during the Y-123melt texturing. We demonstrate that the addition of silver to Y-123 always led to an enhanced texture. The typical microstructure of the composite Y-123 plus Y-211 (that is believed essential for high critical currents in these High Tc superconductors) was not disturbed by addition of silver up to 7.5 wt%, while higher concentrations of metal led to a degradation of the texture. DTA–TG analysis was used to investigate the influence of Ag and Ag(In) alloy on the Y–Ba–Cu–O equilibria around the Y-123 phase. We found a very unexpected thermal behaviour, similar to an eutectic equilibrium, when the silver concentration was increased to35 wt%. We believe that this effect was essentially due to the increasingly higher concentration of silver that could react with the secondary phases present in the melt.

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Abstract  

The 124 superconductor YBa2Cu4O8 was prepared from the oxalate precursor Y2(C2O4)3. ·4BaC2O4·8CuC2O4·xH2O at one atmosphere oxygen pressure. In O2 the precursor decomposes in one step at 300°C and more gradually (300°–600°C) in Ar. The stability of the superconductor is strongly dependent on the gas atmosphere: in O2 and in air there is no significant weight change as long as the temperature does not exceed 800°C, whereas in a 1% O2-99%N2 mixture decomposition starts at about 670°C with the formation of CuO and YBa2Cu3Ox withx<7. The reduction of YBa2Cu4O8 in a 5% H2-95% Ar mixture takes place in at least four major steps with formation of products such as Y2O3, BaO, Cu2O, Cu, BaY2O4 and Ba4Y2O7.

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Abstract  

The thread that runs through all research in the field of superconductivity is new physics through discovery of new materials. The knowledge of superconducting materials has become voluminous and complex. The comprehensive review of the superconducting materials is of particular importance. The main purpose of this report is to present the results of classification for chalcogenide superconductors. Superconducting critical temperature T c, crystal-structure type and the references proper to these compounds are summarized. Brief survey of the superconductivity in chalcogen elements is also given. Furthermore, as representative sulfide and selenide, superconducting characteristics of CuRh2S4 and CuRh2Se4 will be shown.

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The high temperature superconductors of the system Bi-Pb-Sr-Ca-Cu-O show promising properties and large scale applications can be considered. The (Bi,Pb)2Sr2Ca2Cu3O10+δ (Bi,Pb(2223)) phase is attractive because of its high superconducting temperature (110 K) and high current transport capabilities.

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A numerical study of the thermodynamic properties of a superconducting quantum cylinder in a longitudinal magnetic field is carried out. Closed-form expressions for the critical temperature, the free energy, the heat capacity jump, and the magnetization difference between the superconducting and normal phases as functions of the nanotube parameters are obtained in limit cases.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: E. Kuzmann, Z. Homonnay, A. Vértes, I. Halász, J. Bánkuti, and I. Kirschner

Abstract  

151Eu,119Sn and57Fe Mössbauer spectroscopy was used to study high Tc superconductors. Mössbauer spectra of Sn substituted EuBa2Cu3O7–y, YBa2Cu3O7–y and TlBaCaCuO4.5+y as well as of Fe Substituted TlBaCaCuO4.5+y were compared. The Sn and Fe ions replace the regular Cu positions in the YBa2Cu3O7–y and in TlBaCaCuO4.5+y materials, fespectively, while the localization of tin atoms in both the119Sn doped EuBa2Cu3O7–y and TlBaCaCuO4.5+y superconductors is different from that of previous cases. Up to our knowledge, this is the first publication on a Mössbauer study of a Tl-containing superconductor.

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Abstract  

The termal stabilities of several families of high-T c superconductors (HTSC), as well as the dependence of phase transitions on temperature and stoichiometry, have been studied by X-ray diffraction, DTA, TG and DSC. Experimental results are discussed in the context of decomposition models.

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Summary Specific heat data and their relation to the form of the energy gap are reviewed for Al, HfV2, and two recently discovered superconductors, MgB2 and Na0.3CoO2·1.3H2O. The data for Al and HfV2 exemplify the specific heat of, respectively, weak- and strong-coupled BCS superconductors with isotropic energy gaps. MgB2 is also known to be a BCS superconductor, but the specific heat deviates from BCS behavior in a way that shows the presence of two distinctly different energy gaps and characteristics of both weak and strong coupling. The heat capacity of Na0.3CoO2·1.3H2O is strongly sample dependent, but suggests that it is another two-gap, possibly ‘unconventional’ superconductor.

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