Unit cell of ordered -eucryptite containing 12 formula units of (84 atoms). It consists of parallel double helices of interconnected tetrahedra (tan) and tetrahedra (gray), with Li atoms in the spaces between them along the c axis
Number of point defects as function of time, for two different radiation rates, namely, 0.2 PKA/ps (blue) and 1 PKA/ps (red): (a)–(d) vacancies, (e)–(h) antisites, and (i)–(l) interstitials. The time domain over which exposure to radiation is simulated is shown in gray in each plot, and is followed by annealing at 900 K and ambient pressure.
Snapshots of vacancies, antisites, and interstitials of all atom species except Li immediately after the radiation dose (t = 50 ps) and towards the end of the subsequent relaxation (t = 93 ps) for the rates of 0.2 PKA/ps (a) and (b) and 1 PKA/ps (c) and (d). During relaxation, structural recovery (healing) via defect annihilation can be observed at both the rates.
Radial distribution functions ( ) for (a) Al–O and (b) Si–O in pristine -eucryptite at 900 K (black) and in the phase obtained after exposure and relaxation for two radiation rates, 0.2 PKA/ps (blue) and 1 PKA/ps (red). The radial distribution functions curves do not change significantly upon exposure, indicating that the basic network of tetrahedra in -eucryptite is preserved to a large extent.
Radial distribution functions ( ) for (a) Li–O and (b) Li–Li pairs in pristine -eucryptite at 900 K (black) and in the phase obtained after radiation exposure and relaxation for two different rates, 0.2 PKA/ps (blue) and 1 PKA/ps (red). The first peak of shifts from 3.8 Å in -eucryptite to 2.9 Å in the radiated structures, which indicates Li–Li bonding.
Snapshots of structure of (a) pristine -eucryptite at 900 K and (b) phase obtained under exposure at 1 PKA/ps and relaxation. This phase consists of polyhedra with different O coordinations around Si and Al, namely, (tan), (gray), (green), and (red). The Li atoms are shown in purple.
Comparison of the number of (a) AlO and (b) SiO polyhedra of different O-coordination in -eucryptite at 900 K with those in the radiated structures at the end of the radiation dose (t = 50 ps) and towards the end of the subsequent annealing (t = 93 ps).
Angular distribution functions ( ) for angles the defined in panels (a). Shown here are functions for (b) O–Si–O, (c) O–Al–O, (d) Al–O–Si, (e) O–Si–Al, and (f) O–Al–Si angles in -eucryptite (black) and in the phase obtained under radiation exposure at two different rates.
Mechanism for recovery of from in the radiated structure (a) during annealing at 900 K and 1 atm via intermediate steps (b)–(e) leading to the restoration of tetrahedral arrangement of silicon (f).
Article metrics loading...
Full text loading...