# Gibbs energies of formation of rare earth $MPt_5$ compounds

Jacob, KT and Waseda, Y (1990) Gibbs energies of formation of rare earth $MPt_5$ compounds. In: Thermochimica Acta, 165 (2). pp. 223-233.

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## Abstract

The Gibbs energies of formation of $MPt_5 (M\equiv$ Nd, Dy, Ho, Er) intermetallic compounds were determined in the temperature range 900–1100 K using the solid state cell Ta,$M+MF_3|CaF_2|MPt_5+Pt+MF_3,$Ta For $M \equiv$ Sm, a mixture of $Gd + GdF_3$ was used as the reference electrode. In the case of Eu, a mixture of $Eu + EuF_2$ served as the reference electrode. The trifluorides of Sm and Eu are not stable in equilibrium with the metal. The fluoride phase coexisting with a $SmPt_5 + Pt$ mixture is $SmF_3,$ whereas $EuF_2$ is the equilibrium phase in contact with $EuPt_5 + Pt$. All the $MPt_5$ compounds studied (except $EuPt_5)$ exhibit similar stability. Europium is divalent in the pure metal and trivalent in $EuPt_5$. The energy required for the promotion of divalent Eu to the trivalent state accounts for the less negative Gibbs energy of formation of $EuPt_5$. The enthalpies of formation of all the $MPt_5$ compounds obtained in this study are in good agreement with Miedema's model.

Item Type: Journal Article Copyright of this article belongs to Elsevier Science B.V. Gibbs energies Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) CA Sharada 14 Dec 2007 19 Sep 2010 04:41 http://eprints.iisc.ac.in/id/eprint/12528