Structure and cation ordering in La2UO6, Ce2UO6, LaUO4, and CeUO4 by first principles calculations

L. Casillas-Trujillo, H. Xu, J. W. McMurray, D. Shin, G. Baldinozzi, K. E. Sickafus

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

In the present work, we have used density functional theory (DFT) and DFT+U to investigate the crystal structure and phase stability of four model compounds in the Ln2O3-UO2-UO3 ternary oxide system: La2UO6, Ce2UO6, LaUO4, CeUO4, due to the highly-correlated nature of the f-electrons in uranium. We have considered both hypothetical ordered compounds and compounds in which the cations randomly occupy atomic sites in a fluorite-like lattice. We determined that ordered compounds are stable and are energetically favored compared to disordered configurations, though the ordering tendencies are weak. To model and analyze the structures of these complex oxides, we have used supercells based on a layered atomic model. In the layer model, the supercell is composed of alternating planes of anions and cations. We have considered two different ordering motifs for the cations, namely single species (isoatomic) cation layers versus mixed species cation layers. Energy differences between various ordered cationic arrangements were found to be small. This may have implications regarding radiation stability, since cationic arrangements should be able to change under irradiation with little cost in energy.

Original languageEnglish
Pages (from-to)201-213
Number of pages13
JournalComputational Materials Science
Volume123
DOIs
StatePublished - Oct 1 2016

Funding

This work was performed under grant number DE-NA0001983 from the Stewardship Science Academic Alliances (SSAA) of the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) . The views expressed here are those of the authors and do not necessarily reflect those of the DOE, NNSA, or the SSAA. Research partially supported by the U.S. Department of Energy Office of Nuclear Energy, Nuclear Energy Advanced Modeling and Simulation Program . This research used computing resources of the National Institute for Computational Sciences at UT under contract UT-TENN0112 .

Keywords

  • Ab initio calculations
  • Density functional theory
  • Oxides
  • Rare-earth

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