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High-temperature resistivity of the Ba2YCu3Ox superconductor (1987)

Grader, G. Sageev ; Gallagher, P. K. ; Gyorgy, E. M.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 51 (1987), S. 1115-1117

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: The resistivity of Ba2YCu3Ox was measured in the 450–850 °C range at various oxygen partial pressures. The tetragonal to orthorhombic phase transition is observed as a change in the slope of the resistivity curve. The lack of a discontinuity in the curve is consistent with the phase transition being higher than first order. It was found that decreasing the oxygen content x below 6.2 changed the resistivity of the tetragonal phase from metallic character to semiconducting character. In the metallic region of the tetragonal phase the superconducting transition temperature is depressed below 60 K, while in the semiconducting region, no superconducting onset was observed down to 6 K. In the orthorhombic phase, the resistivity of the material is shown to be governed by the number of oxygens per unit cell, suggesting that the resistivity can serve as a quality control parameter in the production of superconducting devices.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.98757

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Superconductivity and microstructures of fluorinated and chlorinated YBa2Cu3Oz (1989)

Yan, M. F. ; Grader, G. Sageev ; Rhodes, W. W. ; [et al.]

Springer

Journal of materials science 24 (1989), S. 703-707

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Superconductivity and microstructures of fluorinated and chlorinated YBa2Cu3O z were investigated with BaF2 and BaCl2 as the fluorination and chlorination agents. The incomplete decomposition of BaF2 and BaCl2 led to inhomogeneous phase and elemental distributions as shown by energy dispersive analysis of X-rays (EDAX) and X-ray diffraction (XRD) analysis. A high (y ⩾ 2) chlorine concentration stabilized a tetragonal perovskite structure in the YBa2Cu3Cl y O z compositions while an orthorhombic structure was observed in samples with a lower chlorine concentration. The maximum superconductivity transition temperature,T c, was ⩽ 95 K in these fluorinated and chlorinated samples. Thus, our data are contradictory to the claims of high transition temperatures (155 K) recently reported for some of these compositions. The microstructural and phase composition data reported here could provide useful information in the search for possibly highT c phases in these fluorinated and chlorinated compositions.