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Nonstoichiometry, defects and thermodynamic properties of YFeO3, YFe2O4 and Y3Fe5O12

Jacob, KT and Rajitha, G (2012) Nonstoichiometry, defects and thermodynamic properties of YFeO3, YFe2O4 and Y3Fe5O12. In: SOLID STATE IONICS, 224 . pp. 32-40.

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Official URL: http://dx.doi.org/10.1016/j.ssi.2012.07.003

Abstract

Oxygen nonstoichiometry of three ternary oxides. YFeO3-delta, YFe2O4-alpha and Y3Fe5O12-theta. in the system Y-Fe-O was investigated as a function of oxygen partial pressure by thermogravimetry at high temperature. The defects responsible for nonstoichiometry were identified as oxygen vacancies for YFeO3-delta and YFe2O4-alpha although the manner of variation of nonstoichiometric parameter with oxygen partial pressure for these two oxides is quite different. Cation interstitials are the predominant defects in Y3Fe5O12-theta. Gibbs energies of formation of the three nonstoichiometric oxides were determined using solid-state electrochemical cells in the temperature range from 975 to 1475 K. YFe2O4-alpha was found to be stable only above 1391 K. Gibbs energies of formation of the three stoichiometric compounds from their component binary oxides were obtained by combining information from solid state cells with results of thermogravimetric analysis using the Gibbs-Duhem relation. The results can be summarized as: (1/2)Y2O3 + (1/2)Fe2O3 -> YFeO3;Delta G(f(ox))(O)(+/- 250)(J/mol) = 17, 126-8.263T (1/2)Y2O3 + FeO + (1/2)Fe2O3 -> YFe2O4;Delta G(f(ox))(O)(+/- 260)(J/mol) = -10,352-13.24T (3/2)Y2O3 + (5/2)Fe2O3 -> Y3Fe5O12;Delta G(f(ox))(O)(+/- 780)(J/mol) = -56, 647-31.091T. (C) 2012 Elsevier B.V. All rights reserved.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to Elsevier
Keywords: Gibbs free energy; Enthalpy; Entropy; Yttrium orthoferrite; Yttrium iron garnet; Buffer electrode
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Depositing User: Id for Latest eprints
Date Deposited: 11 Jan 2013 09:13
Last Modified: 11 Jan 2013 09:13
URI: http://eprints.iisc.ac.in/id/eprint/45271

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