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1043-T06-03-E06-03

Insights into Radiation Tolerance of Ceramics from Large Scale Molecular Dynamics Simulations

Ram Devanathan and William J. Weber and Materials Sciences Division © 2008Chemical Materials Research Society Pacific Northwest National Laboratory, Richland, WA

Motivation Fundamental study of defect phenomena in ceramics

Issues: We are interested in defect processes in: Nuclear fuels and inert matrices Ceramic nuclear waste forms

© 2008 Materials Research Society We need to understand fundamentals of defect production and annealing. Why are some ceramics more radiation tolerant than others?

R. Devanathan and W. J. Weber

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Scope Comparison of primary damage state produced by heavy ion recoils in ZrO2,YSZ and ZrSiO4 under similar conditions

© 2008 Materials Research Society

R. Devanathan and W. J. Weber 3

Why YSZ? Yttria stabilized zirconia is highly radiation tolerant

·· V Substituting Y2O3 for ZrO2 introduces O

' + V ·· + 2ZrO x x Y O + 2Zr + O → 2Y ©22008 Materials Research 3 Zr O Zr O Society 2 Radiation damage simulations seldom account for pre-existing defects Our work compares pure ZrO2, YSZ and ZrSiO4 R. Devanathan and W. J. Weber 4

Details of our MD simulations 1,117,200 atoms (ZrSiO4) or 1,500,000 atoms (ZrO2) Buckingham potentials1,2 fitted to ZBL repulsive potential3 DL_POLY3 code (parallel MD) NPT equilibration at 300 K for 3 ps. © keV 2008 Research Society 30 Zr orMaterials U recoil along [001], [110] or [111]

NVE simulation for 25 ps 1R.

Devanathan et al, PRB 69:064115 (2004) 2P. K. Schelling et al, J. Am. Ceram. Soc. 84:1609 (2001). 3J. F. Ziegler et al, The stopping and range of ions in matter (Pergamon, NY, 1985).

R. Devanathan and W. J. Weber

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Atoms displaced by more than 2 Å 30 keV Zr in ZrO2 and YSZ : [001] recoil in ZrO2 : [001]; : [110];

30 keV Zr in ZrSiO4

: [111] YSZ

© 2008 Materials Research Society

# of displacements is comparable. This can be misleading. R. Devanathan and W. J. Weber

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30 keV Zr recoil in ZrSiO4 at 22 ps # of surviving defects > # of atoms displaced ballistically!

© 2008 Materials Research Society

115 Å x 70 Å Nearly 24% of defects are in amorphous clusters. ~4300 defects survive. R. Devanathan and W. J. Weber

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30 keV Zr recoil in 10 % YSZ at 24 ps

© 2008 Materials Research Society

A few isolated defects. No defect clusters

R. Devanathan and W. J. Weber

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30 keV [001] Zr recoil in ZrSiO4

© 2008 Materials Research Society

Defects were defined based on change in CN and neighbor environment Defect accumulation and in-cascade amorphization.

R. Devanathan and W. J. Weber 9

30 keV [001] Zr recoil in ZrO2

© 2008 Materials Research Society

Defects were defined based on occupation of Wigner cells. Remarkable defect recovery; only ~50 defects remain.

R. Devanathan and W. J. Weber 10

30 keV Zr recoils in YSZ

© 2008 Materials Research Society

Anion interstitials in red; Cation interstitials in blue Complete recovery on anion sublattice

R. Devanathan and W. J. Weber 11

30 keV [001] Zr recoil in YSZ at 24 ps

© 2008