Radiation effects and tolerance mechanism in beta-eucryptite
B Narayanan and IE Reimanis and HC Huang and CV Ciobanu, JOURNAL OF APPLIED PHYSICS, 113, 033504 (2013).
Previous studies on Li-silicates have shown that these materials are resistant to radiation damage even in extreme physical and chemical environments, and are thus promising solid-state breeder materials in fusion reactors. Here, we focus on beta-eucryptite as a member of Li-Al silicate class of ceramics with potential for nuclear applications, and study the atomic-scale processes induced by radiation. Using molecular dynamics simulations based on a reactive force field, we have found that upon radiation dosage of 0.21 displacements-per-atom or less, the structure largely retains its long-range order while exhibiting (a) disordering of the Li atoms, (b) distortion of the Si and Al tetrahedra defined as the change in their oxygen-coordination number, and (c) tilting of the Si and Al tetrahedra with respect to one another. We find that Si tetrahedra that distort to SiO3 during exposure to radiation recover significantly upon thermal relaxation, and provide the mechanism for this recovery. This mechanism consists in the tilting of AlO5 polyhedra formed upon exposure so as to satisfy the oxygen-coordination of distorted Si tetrahedra. Doubling the dosage results in a significant increase of the concentration of Si-Al antisite defects, which renders the tolerance mechanism inefficient and leads to amorphization. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4775838
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