Role of interfaces in damage process of irradiated lithium aluminate nanocrystals

Abstract

Molecular dynamics simulations were performed to understand the differences in the response of single crystal and nanocrystalline γ‐LiAlO2 to energy deposition by 10 keV Li recoils. The simulations are performed at 573 K and focus on the damage production in the absence of thermal annealing. The grain boundaries in the nanocrystals are found to be amorphous. Analyses of the fate of the beam ions show that the amorphous grain boundaries and differently oriented nanograins increase the number of backscattered ions and decrease the number of transmitted ions. Damaged regions protruding from the grain boundaries provide a direct evidence of the role of the grain boundaries as scattering centers in collision cascades. The simulations show that the defect density produced in the nanocrystals is about twice that in the single crystals. In both samples, Li defects account for 70% of the defects, demonstrating that LiO4 tetrahedra are much more susceptible to damage than AlO4 tetrahedra. Furthermore, Li defects occur preferentially near grain boundaries. Diffusion simulations confirm the limited thermal diffusion of defects at 573 K, effectively separating the damage production from thermal annealing in the irradiation simulations. Nevertheless, the mean square displacements of grain‐boundary defects are found to be larger than lattice defects and surface defects.

Molecular dynamics simulations of displacement cascades in LiAlO 2 and LiAl 5 O 8 ceramics

“…For Al and O at 5, 10 and 15 keV in Fig.6 (d), (e) & (f) and Fig.6(g), (h) & (i) respectively, the number of Frenkel pairs in LiAlO 2 was consistently 1.5-2 times higher than in LiAl 5 O 8 . From these observations, it is clear that in LiAlO 2 , the Li sublattice experienced the most damage, which was up to 60% of the total damage, consistent with the observations in ref 11. .…”

“…With regards to MD potentials for the LiAlO 2 system, Jacob et al developed a potential in 1996 14 and Tsuchihira − Oda − Tanaka 15 developed another potential in 2009. Jacob's potential did not generate a stable structure 11 and was not considered for our work. The TOT potential has been well established for the LiAlO 2 system but the charges in the TOT potential are 0.7 for Li, -1.1 for O and 1.5 for Al, which is not transferrable to the LiAl 5 O 8 system because the charges would not add up to zero.…”

“…Li defects are predominant due to the low displacement energy of 22 eV for Li in comparison to 84 eV for aluminum and 37 eV for oxygen. A recent MD study investigated irradiation damage in γ-LiAlO 2 and found that Li defects account for about 70% of the damage and LiO 4 tetrahedra are more susceptible to damage than the AlO 4 tetrahedra 11 . Although there has been computational and experimental research into the radiation response of γ-LiAlO 2 , much less is known about these phenomena in LiAl 5 O 8 .…”

Raman study of amorphization in nanocrystalline 3C–SiC irradiated with C+ and He+ ions

“…In fact, in that region including GBs, atomic displacements are easier to be created due to the disordered structure that lowers the threshold displacement energies . In addition, GBs can act as effective scattering centers in displacement cascades and further increase the number of atomic displacements near GBs . These atomic displacements can stimulate preferential amorphization at GBs from the amorphous SiC matrix to the grain interior.…”

First-Principles Study of Tritium Trapping in γ-LiAlO2 Nanovoids

“…Consequently, in order to improve the fundamental understanding of microstructure evolution occurring in TPBARs during irradiation and its effects on tritium diffusion, several computational studies were performed and a series of post-irradiation (from both neutron and ion irradiation) examinations was conducted for the various components of the TPBAR. In the specific case of γ-LiAlO 2 pellets, the combination of neutron flux and thermalization of high-energy 4 He and T products from 6 Li fission can induce various defects and changes in the material such as amorphization of grain boundaries (GBs) and material decomposition − and point defects such as cation and anion vacancies and interstitials. ,,− After thermalization, radioactive tritium, which has a half-life of 12.3 years, can be considered as an impurity diffusing in the pellet and the other parts of the TPBAR. In the design of the TPBAR, the γ-LiAlO 2 pellets are sandwiched between an inner zircaloy liner and an outer nickel-plated zircaloy tritium getter, whose role is to capture the tritium generated from the pellets.…”