Gibbs energy of formation of CuGd{sub 2}O{sub 4} and phase relations in the Cu-Gd-O system
- Univ. of Leeds (United Kingdom). Dept. of Mining and Mineral Engineering
Oxygen potentials for the coexistence of Cu{sub 2}O + Gd{sub 2}O{sub 3} + CuGd{sub 2}O{sub 4}, Cu{sub 2}O + CuO + CuGd{sub 2}O{sub 4}, and Cu + Cu{sub 2}O + Gd{sub 2}O{sub 3} three-phase equilibrium have been measured between 960 and 1,290 K, receptively. The results obtained in this study indicate that the ternary phase, CuGd{sub 2}O{sub 4}, is nearly stoichiometric. The measured oxygen potentials for the coexistence of various three-phase assemblages are given by the expressions {Delta}{mu}{sub O{sub 2}} = {minus}254319.6 + 163.813T ({+-}200) J/mol; {Delta}{mu}{sub O{sub 2}} = {minus}261380 + 187.745T ({+-}200) J/mol; and {Delta}{mu}{sub O{sub 2}} = {minus}334728 + 143.741T ({+-}50) J/mol between 960 and 1,290 K, respectively. Combining the oxygen potentials for the coexistence of Cu{sub 2}O + Gd{sub 2}O{sub 3} + CuGd{sub 2}O{sub 4} with that of Cu{sub 2}O + CuO gives for the reaction CuO(s) + Gd{sub 2}O{sub 3}(s) {yields} CuGd{sub 2}O{sub 4}(s); {Delta}G{degree} = 1580.1 {minus} 5.957T ({+-}200) J/mol. The results obtained in the present investigation suggest that the formation of CuGd{sub 2}O{sub 4} from component oxides is slightly endothermic and the phase CuGd{sub 2}O{sub 4} is an entropy-stabilized compound. The enthalpy and entropy of formation of CuGd{sub 2}O{sub 4} from component oxides obtained in this study are in excellent agreement with the recent calorimetric data. Phase relations and oxygen-potential diagram for the Cu-Gd-O ternary system have been constructed at 1,273 K by combining the results obtained in this study and the auxiliary thermodynamic data available in the literature.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 103619
- Journal Information:
- Journal of the American Ceramic Society, Vol. 78, Issue 7; Other Information: PBD: Jul 1995
- Country of Publication:
- United States
- Language:
- English
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