Gibbs energy of formation of Cu{sub 2}Yb{sub 2}O{sub 5} and thermodynamic stability of Cu{sub 2}R{sub 2}O{sub 5} (R = Tb-Lu)
- Univ. of Leeds (United Kingdom)
The electromotive force (emf) of the solid oxide electrochemical cell, (-)Pt/Cu{sub 2}O + Yb{sub 2}O{sub 3} + Cu{sub 2}Yb{sub 2}O{sub 5}//(CaO)ZrO{sub 2}//O{sub 2}(P = 0.0212 MPa)/Pt(+), has been measured between 960 and 1320 K. Based on the measured emf of the above cell as a function of temperature, the Gibbs energy change for the reaction 2Cu{sub 2}O(s) + 2Yb{sub 2}O{sub 3}(s) + O{sub 2}(g) {yields} 2Cu{sub 2}Yb{sub 2}O{sub 5}(s) is obtained as {Delta}G{degrees} = {minus}231,225 + 151.847T ({plus_minus}200) J mol{sup {minus}1}. The Gibbs energy change for the above reaction when combined with that for Cu{sub 2}O + CuO equilibrium from the literature gives, for the reaction 2CuO(s) + Yb{sub 2}O{sub 3}(s) + Yb{sub 2}O{sub 3}(s) {yields} Cu{sub 2}Yb{sub 2}O{sub 5}(s), {Delta}G{degrees} = 17,128 {minus} 20.07T ({plus_minus}100) J mol{sup {minus}1}. It can be seen that the formation of Cu{sub 2}Yb{sub 2}O{sub 5} from the component oxides is endothermic. Since Cu{sub 2}Yb{sub 2}O{sub 5} is an entropy stabilized compound and its formation is endothermic from component oxides, Cu{sub 2}Yb{sub 2}O{sub 5} is thermodynamically unstable relative to its component oxides below 853 K. Earlier we reported the Gibbs energy of formation of Cu{sub 2}Dy{sub 2}O{sub 5}, Cu{sub 2}Ho{sub 2}O{sub 5}, and Cu{sub 2}Er{sub 2}O{sub 5} from CuO and R{sub 2}O{sub 3}(R = Dy, Ho, Er). Since Cu{sub 2}Yb{sub 2}O{sub 5} is also a member of the Cu{sub 2}R{sub 2}O{sub 5} family of compounds whose crystal structure belongs to a noncentrosymmetric space group P2{sub 1}nb, an attempt has been made to correlate their thermodynamic properties such as enthalpy and entropy of formation with the ionic radius of the trivalent rare-earth cation present in octahedral coordination. Based on this correlation, {Delta}H, {Delta}S, and {Delta}G for the formation of Cu{sub 2}Tb{sub 2}O{sub 5}, Cu{sub 2}Tm{sub 2}O{sub 5}, and Cu{sub 2}Lu{sub 2}O{sub 5} from the component oxides have been estimated.
- OSTI ID:
- 450699
- Journal Information:
- Journal of Solid State Chemistry, Vol. 125, Issue 1; Other Information: PBD: Aug 1996
- Country of Publication:
- United States
- Language:
- English
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