Standard free energies of formation of rare earth sesquisulphides

Akila, R and Jacob, KT and Shukla, AK (1987) Standard free energies of formation of rare earth sesquisulphides. In: Journal of Materials Science, 22 (6). pp. 2087-2093.

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Abstract

An e.m.f. technique was used for the measurement of the Gibbs' energy changes involved in the conversion of the rare earth oxysulfides to the corresponding sesquisulfides at 870-1120 K. The cell arrangement is Au, Ag + $Ag_2S|R_20_2S$ + $R_2S_3||$ $(Y_2O_3)ThO_2||Fe$ + $Fe_{0.95}O$, Au where R = La, Pr, Nd, Sm, Eu and Gd. Yttria-doped thoria is used as the solid electrolyte because it has predominant ionic conduction at the low oxygen potentials developed at the $R_2O_2S + R_2S_3$ electrode, especially for systems containing heavier rare earth elements. The sulphur potential at the left-hand electrode is established by the dissociation of $Ag_2S$ to silver in a closed system. The changes in the standard free energy, enthalpy and entropy associated with the conversion of the rare earth oxysulphide to the sesquisulphide all show a smooth variation with rare earth atomic number. Based on these empirical trends, the corresponding thermodynamic functions for terbium, dysprosium and holmium systems are estimated. The measured free energy values are combined with recent data on the standard free energies of formation of the rare earth oxysulphides to obtain the Gibbs' energies of formation of the corresponding sesquisulphides.

Item Type:	Journal Article
Publication:	Journal of Materials Science
Publisher:	Springer
Additional Information:	Copyright for this article belongs to the Springer.
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	08 May 2008
Last Modified:	07 Oct 2010 11:24
URI:	http://eprints.iisc.ac.in/id/eprint/13893

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