Abstract
Nano-sized Y2Ti2O7 and Y2TiO5 are primary precipitates in nano-structured ferritic alloys (NFAs). We report a first-principles study on the stabilities of polar Y2Ti2O7 surfaces, and also the selective helium trapping in NFAs. Results show that (1) all variants of Y2Ti2O7 (110) surfaces were found to be more stable than the (100) surfaces, and non-stoichiometric Y2Ti2O7 (110) surfaces are always more stable than their stoichiometric counterparts. (2) The radiation induced helium prefers the octa-interstitial sites in Y2Ti2O7 (or the open-channel along the b-axis of Y2TiO5) to vacancies in the iron matrix. (3) The He-He interaction in Y2Ti2O7 is essentially repulsive. Helium dispersion would largely depend on the number and dispersion of these nano-oxides in NFAs. (4) Charge transfer occurs only between helium and neighboring oxygen anions, suggesting the generality of trapping helium in oxides. Helium trapping at the Fe(100) /Y2Ti2O7(100) interface were also investigated.
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