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  • 1
    Electronic Resource
    Electronic Resource
    Effects of high oxygen pressures and temperatures on the stability of the three superconducting Y-Ba-Cu-O compounds (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3673-3678 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the course of investigating synthesis routes, stability information was developed for YBa2Cu3O7−x, Y2Ba4Cu7O15−x, and YBa2Cu4O8. The results were obtained between ∼900 and 1040 °C and involve oxygen pressures between 10 and 145 atm. The observations show that the PO2-T ranges for stability of the three phases overlap and that some stable mixtures of the phases can be synthesized. The results are compared to the results of other experimental studies and to calculations based on calorimetric data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357431
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  • 2
    Electronic Resource
    Electronic Resource
    Anisotropic hardness and fracture toughness of highly aligned YBa2Cu3O7−δ (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2363-2367 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hardness and fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., Kc001〈Kc100 or Kc010. Indentation crack length measurements on the (001) basal plane with the impression diagonals oriented parallel to the [100] and the [010] directions, indicate that the fracture toughness of these planes is K100/010air∼0.7 MPa m1/2. The hardness in this orientation was found to be 6.7 GPa. Measurements on a plane perpendicular to the basal plane resulted in a lower hardness of ∼3.8 GPa. This reduction in hardness is influenced by the extensive preferential cleavage of the (001) basal plane boundaries. The extremely low values of the fracture toughness suggest that considerable toughening would have to be achieved in melt-textured 123 for any practical bulk application. The presence of 211 phase and silver particles may serve to enhance the fracture toughness of aligned 123 by crack deflection and crack tip blunting respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351090
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  • 3
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    An automated system for current–voltage characterization of ceramic superconductors (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 3187-3192 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An automated system for determinations of transport current–voltage (I–V) characteristics as a function of temperature (25–125 K), magnetic field (0–1.6 T), and magnetic field orientation (−125 to +145°) is described. Currents of up to 100 A are applied either as a continuous ramp or as pulses of 2–100 ms duration. A closed-cycle helium refrigerator provides a rapid (∼45 min), convenient, cost effective, cooldown from 300 to 25 K. Control of current, temperature, magnetic field, and field orientation is fully automated and requires no user interaction. The characterization of performance of a ceramic superconductor typically involves several temperatures, fields, and orientations and requires 8–30 h to complete. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147443
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  • 8
    Electronic Resource
    Electronic Resource
    Grain-boundary compositions in YBa2Cu3O7−x from Auger electron spectroscopy of fracture surfaces (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 331-335 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Comparison of Auger electron spectra obtained from intergranular and transgranular areas exposed on fracture surfaces of sintered YBa2Cu3O7−x specimens indicates that most grain-boundary surfaces are deficient in oxygen and rich in copper compared to the bulk. The thickness of this region of altered composition is estimated to be in the range of 15–50 A(ring). No evidence of segregation of impurities to grain boundaries was seen. The results suggest that the grain-boundary layer is nonsuperconducting and a likely contributor to the problem of low critical current densities in these materials. It is believed that carbon at grain boundaries which has been reported results from incomplete calcination in material which is slightly off stoichiometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341432
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  • 9
    Electronic Resource
    Electronic Resource
    Phase stability for the in situ growth of Nd1+xBa2−xCu3Oy films using pulsed-laser deposition (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 96-98 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have determined the stability line in the 1/T−log[P(O2)] phase space for the synthesis of Nd1+xBa2−xCu3Oy (NdBCO) films. A systematic study of Tc, Jc, and ρ(T) dependence on oxygen partial pressure and temperature for the deposition of thin NdBCO films grown by pulsed-laser deposition was performed. The conditions for optimal NdBCO film growth were determined by varying oxygen partial pressure from 0.02 to 400 mTorr, and substrate temperature between 730 and 800 °C. The results show that the best NdBCO films are obtained at oxygen pressures in the range of 0.2–1.2 mTorr, depending on the substrate temperature. This is more than two orders-of-magnitude lower than the correspondent oxygen pressure appropriate for YBa2Cu3O7−δ film growth. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123162
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of texture on grain boundary misorientation distributions in polycrystalline high temperature superconductors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 711-713 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Computer simulations were performed to determine the most probable grain boundary misorientation distribution (GBMD) in model polycrystalline superconductors. GBMDs in polycrystalline superconductors can be expected to dictate the macroscopic transport critical current density, Jc. Calculations were performed by simulating model polycrystals and then determining the GBMD. Such distributions were calculated for random materials having cubic, tetragonal, and orthorhombic crystal symmetry. In addition, since most high temperature superconductors are tetragonal or pseudotetragonal, the effect of macroscopic uniaxial and biaxial grain orientation texture on the GBMD was determined for tetragonal materials. It is found that macroscopic texture drastically alters the grain boundary misorientation distribution. The fraction of low angle boundaries increases significantly with uniaxial and biaxial texture. The results of this study are important in correlating the macroscopic transport Jc with the measured grain orientation texture as determined by x-ray diffraction © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116600
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