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Issue 40, 2014
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Thermodynamics of thorium substitution in yttrium iron garnet: comparison of experimental and theoretical results

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Abstract

The thermodynamic stability of Th-doped yttrium iron garnet (Y3Fe5O12, YIG) as a possible actinide-bearing material has been investigated using calorimetric measurements and first-principles electronic-structure calculations. Yttrium iron garnet with thorium substitution ranging from 0.04 to 0.07 atoms per formula unit (Y3−xThxFe5O12, x = 0.04–0.07) was synthesized using a citrate–nitrate combustion method. High-temperature oxide melt solution calorimetry was used to determine their enthalpy of formation. The thermodynamic analysis demonstrates that, although the substitution enthalpy is slightly endothermic, an entropic driving force for the substitution of Th for Y leads to a near-zero change in the Gibbs free energy. First-principles calculations within the density functional theory (DFT) indicate that the main limiting factors for Th incorporation into the YIG structure are the narrow stability domain of the host YIG and the formation of ThO2 as a secondary phase. Nevertheless, the defect formation energy calculations suggest that by carefully tuning the atomic and electronic chemical potentials, Th can be incorporated into YIG. The thermodynamic results, as a whole, support the possible use of garnet phases as nuclear waste forms; however, this will require careful consideration of the repository conditions.

Graphical abstract: Thermodynamics of thorium substitution in yttrium iron garnet: comparison of experimental and theoretical results

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Publication details

The article was received on 17 Jul 2014, accepted on 13 Aug 2014 and first published on 14 Aug 2014


Article type: Paper
DOI: 10.1039/C4TA03683B
Author version available: Download Author version (PDF)
Citation: J. Mater. Chem. A, 2014,2, 16945-16954
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    Thermodynamics of thorium substitution in yttrium iron garnet: comparison of experimental and theoretical results

    X. Guo, Zs. Rak, A. H. Tavakoli, U. Becker, R. C. Ewing and A. Navrotsky, J. Mater. Chem. A, 2014, 2, 16945
    DOI: 10.1039/C4TA03683B

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