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  • American Institute of Physics (AIP)  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxidation induced decomposition of YBa2Cu3O7−x (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 906-913 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: At low oxygen potentials, YBa2Cu3O7−x decomposes by chemical reactions involving reduction. The results of this study show that the compound also decomposes at higher oxygen potentials. The initial decomposition products were found to be Y2BaCuO5 and a Ba-Cu oxide phase. The Ba-Cu phase was found to be a peroxide-type and the decomposition can be described by a chemical reaction involving oxidation: 4(YBa2Cu3O7−x)+(1/2 − 3/2δ +2x)O2(arrow-right-and-left)2Y2BaCuO5+3Ba2Cu3O6−δ+CuO. At 800 °C the equilibrium pressure for this reaction is slightly 〈1 bar, and the enthalpy change is ∼80-kJ/mol Y123. This result is not consistent with the conclusions drawn from some other studies of the stability of the superconducting Y-Ba-Cu-O compounds, and the differences are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349597
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation and grain boundary chemistry of dense polycrystalline YBa2Cu4O∼8 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2426-2430 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dense polycrystalline samples of the compound YBa2Cu4O∼8, Y124, were prepared by a three-step procedure. In the first step a mixture of Y2O3, CuO and BaO2 was reacted at 960 °C under an oxygen pressure of 55 bar. The compound did not sinter under these conditions but electrical resistivity and susceptibility measurements showed that the oxide mixture converted to Y124. In the second step densification was produced by hot isostatic pressing at 875 °C. This degraded the superconducting properties severely and a final high-temperature anneal in pressurized oxygen was required to restore optimum properties. This anneal consisted of a one hour hold at 1010 °C in 40-bar O2 followed by a 24-h anneal at 950 °C in 55-bar O2. After this treatment the samples were ∼90% dense, phase pure Y124. The maximum grain dimensions were about 10 μm, and Auger spectroscopy data were obtained on a fracture surface. These data showed that the grain boundary composition does not differ significantly from the bulk values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348677
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  • 3
    Electronic Resource
    Electronic Resource
    Some observations of the effects of high pressures and temperatures on the stability of YBa2Cu3O7−x (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6934-6939 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot isostatic pressing and heat treatments in high-pressure oxygen were used to study the effect of pressure on the stability of YBa2Cu3O7−x. At 875 °C the compound decomposes at an oxygen pressure of about 7 bars. The decomposition involves formation of Y2BaCu3O5 and a Ba-Cu oxide phase. Formation of the latter phase involves additional oxidation because this phase can contain as many as 1.5 oxygen atoms per barium atom. The decomposition can most simply be visualized by considering the chemical reaction 2(YBa2Cu3O7−x)+( (1)/(4) +x−y/2)O2→Y2BaCuO5+Ba3Cu5O9.5−y. Encapsulated samples also decompose during hot isostatic pressing, but the process appears to be more complex. The compound YBa2Cu4O8 was detected in addition to the two products observed in oxygen-treated samples. The reaction above, with YBa2Cu3O7−x serving as an oxygen source, aids in understanding the microstructural observations for encapsulated samples. Decomposition can be completely reversed by annealing in air for 20 h at 875 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345088
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  • 4
    Electronic Resource
    Electronic Resource
    Ambient temperature thermal conductivity of YBa2Cu3O7−x (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 6181-6184 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparative method was used to measure the thermal conductivity λ of a YBa2Cu3O7−x sample over the temperature range 305–360 K. Using one sample, data were obtained at two different x levels. Surprisingly, the smaller x value (higher Tc) produced a lower thermal conductivity. This observation is discussed in terms of scattering of phonons by point defects and electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343554
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