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Title: Trapping helium in Y{sub 2}Ti{sub 2}O{sub 7} compared to in matrix iron: A first principles study

Pyrochlore Y{sub 2}Ti{sub 2}O{sub 7} is a primary precipitate phase in nano-structured ferritic alloys (NFAs) for fission and fusion energy applications. We report a theoretical study for assessing the relative stability of trapping helium in Y{sub 2}Ti{sub 2}O{sub 7} versus in matrix iron. Various defect structures and the associated energies are examined and compared. Results reveal that helium can be deeply trapped in Y{sub 2}Ti{sub 2}O{sub 7} and that the corresponding self-interaction is essentially repulsive. Transmutant helium in NFAs prefers to occupy individual octa-interstitial sites in Y{sub 2}Ti{sub 2}O{sub 7}, before forming small clusters in Y{sub 2}Ti{sub 2}O{sub 7}. Helium partitioning in NFAs depends on the number and dispersion of Y{sub 2}Ti{sub 2}O{sub 7}; and thus initially, bubble formation and growth in iron matrix can be largely suppressed. Charge transfer occurs from helium to neighboring oxygen anions, but not to neighboring metal cations, suggesting a general effectiveness of trapping helium in oxides. Reasons for the ultimate fate of helium to form small nm-scale interface bubbles are also discussed.
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [2] ; ;  [3] ; ;  [4]
  1. School of Materials Science and Engineering, Central South University, Changsha 410083 (China)
  2. (China)
  3. Materials Department, University of California, Santa Barbara, California 93106 (United States)
  4. State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083 (China)
Publication Date:
OSTI Identifier:
22273616
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 14; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; ANIONS; CATIONS; COMPARATIVE EVALUATIONS; FERRITIC STEELS; HELIUM; INTERFACES; IRON; MATRIX MATERIALS; NANOSTRUCTURES; PHASE STABILITY; PRECIPITATION; TITANIUM OXIDES; TRAPPING; YTTRIUM COMPOUNDS