# Gibbs' free energies of formation of $Cu_2Ln_2O_5$ (Ln = Tb, Dy, Er, Yb) compounds

Jacob, KT and Mathews, Tom and Hajra, JP (1993) Gibbs' free energies of formation of $Cu_2Ln_2O_5$ (Ln = Tb, Dy, Er, Yb) compounds. In: High Temperature Materials and Processes, 12 (4). pp. 251-258.

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## Abstract

The studies of Gibbs' free energies of formation of compdound of type $Cu_2Ln_2O_5$ (Ln = Tb, Dy, Er, Yb) were measured by using the solid state cell Pt, $Cu_2O$ + $Cu_2Ln_2O_5$ + $Ln_2O_3/(Y_2O_3)ZrO_2/Cu_2O$ + CuO, Pt in the temperature range of 970 to 1323 K. Formation of these compounds is endothermic and the compdounds become thermodynamically unstable with respect to their component oxides < 955 K for $Cu_2Tb_2O_5$, < 850 K for $Cu_2Dy_2O_5$, < 768 K for $Cu_2Er_2O_5$, and < 714 K for $Cu_2Yb_2O_5$. When the oxygen partial pressure over $Cu_2Ln_2O_5$ is lowered, they decomposed according to the scheme, $2Cu_2Ln_2O_5 (s) \rightarrow 2Ln_2O_3 (s) + 2Cu_2O (s) + O_2 (g)$. The equilibrium chemical potentials of oxygen corresponding to the dissociation reactions are computed from the emf data and auxiliary information on $Cu_2O$ and CuO. The computed decomposed temperaute at an oxygen partial pressure of $5.0 \times 103 Pa$ are compared with those obtained directly from combined thermogravimetric and differential thermal analyses (DTA). The free energy, enthalpy and entropy of formation of $Cu_2Ln_2O_5$ compdounds show systematic variation with the ionic radius of the trivalent lanthanide ion. The trends obtained in this study are compared with information available in the literature. The stability of $Cu_2Ln_2O_5$ compdounds increases with the decrease in ionic radii of the $Ln^{3+}$ ion.

Item Type: Journal Article Copyright of this article belongs to Freund Publishing House. Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 08 Jul 2008 19 Sep 2010 04:47 http://eprints.iisc.ernet.in/id/eprint/14833