Drop-tube experiments have been performed on Y x Nd 1−x Ba 2 Cu 3 O y (0.7 ഛ x ഛ 1.0) to understand the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders 50-100 m in diameter were processed in pure O 2 at furnace temperatures of 1575-1800°C, every 25°C. The resulting samples were examined microstructurally by scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was found that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. A decreasing trend in the overall melting temperature with increasing Nd was also identified.
This paper presents the results of drop-tube experiments performed on Y x Nd 1−x Ba 2 Cu 3 O y (0 ഛ x ഛ 0.5) to understand some of the effects of partial substitutions of Nd for Y on the phase relationships in these systems at elevated temperatures. Powders from 50 to 100 m in diameter were processed in pure O 2 at furnace temperatures from 1400 to 1800°C, every 25°C. The resulting samples were examined microstructurally using scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy. Powder x-ray diffraction was performed for phase identification. It was verified that Nd substitution alters phase selection by introducing at least one new phase and allowing for solidification of the superconducting composition directly from the melt via undercooling to below the peritectic transformation temperature. In addition, solidification pathways are altered for samples processed at temperatures just below the liquidus temperature.Microstructural and x-ray diffraction evidence was used to map the liquidus with increasing Nd substitution. It was found that a minimum in this liquidus occurs at or near the composition Y 0.1 Nd 0.9 Ba 2 Cu 3 O x and at a temperature of 1500°C (±25°C).
Containerless processing of YBa2Cu3O7−δ was performed using an aero-acoustic levitation technique. Upon solidification from the liquid, spheres of size 2.5 mm diameter undercooled and recalesced, forming tetragonal YBa2Cu3O7−δ directly from the melt. Subsequent to solidification processing, these samples were annealed to single phase YBa2Cu3O7−δ with orthorhombic symmetry as indicated by powder XRD, SQUID magnetometer measurements indicate a sharp superconducting transition at approximately 85 K. Magnetic Jc values, calculated using the Bean critical state model, indicate that the spheres can carry critical current densities on the order of 104 A cm−2. Microstructural characterization has been performed on both the as-solidified and annealed spheres.
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