Phase equilibria among the superconductors in the Y{sub 2}O{sub 3}{endash}BaO{endash}Cu{endash}O system
- Princeton Materials Institute and Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States)
The enthalpy of formation of Y{sub 2}Ba{sub 4}Cu{sub 7}O{sub 14.864} at room temperature has been determined by using high-temperature reaction calorimetry. The standard enthalpy of formation of the 247 phase is {Delta}H{sup o}{sub f}={minus}5463{plus_minus}18&hthinsp;kJ&hthinsp;mol{sup {minus}1}. Phase relationships among the superconductors, namely, the 123, 124, and 247, are assessed. It is intrinsic that impurity phases, such as Y{sub 2}Cu{sub 2}O{sub 5}, BaCuO{sub 2}, CuO, etc., coexist with the superconductors at equilibrium. Equilibria among the superconductor phases in the Y{sub 2}O{sub 3}{endash}BaO{endash}Cu{endash}O system have been determined. The results show that, at the 124 bulk composition, the 247 phase coexists with the excess CuO in a narrow area of p{sub O{sub 2}}{approximately}T space confined by the stability fields of the 124 phase and a mixture of the 123+CuO. The standard free energies of carbonation and hydration of the 247 phase are also determined, which are {minus}629{plus_minus}13&hthinsp;kJ&hthinsp;mol{sup {minus}1} and {minus}873{plus_minus}45&hthinsp;kJ&hthinsp;mol{sup {minus}1}, respectively. Like the 123 and 124 phases, the 247 phase is thermodynamically unstable for corrosion by water vapor and carbon dioxide in ambient atmosphere. {copyright} {ital 1999 Materials Research Society.}
- OSTI ID:
- 698835
- Journal Information:
- Journal of Materials Research, Vol. 14, Issue 9; Other Information: PBD: Sep 1999
- Country of Publication:
- United States
- Language:
- English
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