Crystal structure of hexagonal ordered β-eucryptite projected (a) along the c axis, and (b) along the a 1 axis. The structure is composed of a framework of corner-sharing AlO4 (gray) and SiO4 (orange) tetrahedra, with Li atoms (purple) existing in channels parallel to the c axis. The black lines outline the unit cell containing 12 formula units of LiAlSiO4 (84 atoms).
Evolution of (a) relative orientation of forces and , and (b) structure factor during the metadynamics simulation of β-eucryptite under hydrostatic pressure of 3 GPa at 300 K. A spike in the relative orientation of and indicates structural transition at step 58.
Evolution of structural parameters of the computational supercell (a) edge lengths, namely, a, b, c, and (b) angles, namely, α, β, and γ during metadynamics. The portion of the run in which the gaussians are turned on (i.e., up to step 58) is shown as the shaded region, while the gaussians are switched off (i.e., W = 0) in the unshaded region.
Simulated XRD spectra for β-eucryptite (black) and the new phase (red) obtained at P = 3 GPa and T = 300 K. The loss of well-defined peaks in the XRD spectrum of the new phase indicates that it is amorphous.
Radial distribution functions of (a) Al–O, (b) Si–O, (c) Li–O, and (d) Li–Li pairs in β-eucryptite (black) and in the new phase (red) obtained under a hydrostatic pressure of 3 GPa at 300 K. In the new phase, the long range ordering is absent indicating amorphization.
Angle distribution functions η for the angles defined in panel (a). The η 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 β-eucryptite (black) and new phase obtained at P = 3 GPa and T = 300 K are shown here.
Comparison of the number of AlO x and SiO x polyhedra of different O-coordinations (i.e., different values of x) in β-eucryptite under ambient conditions and the new phase obtained at 3 GPa and 300 K.
Atomic scale mechanism of amorphization of (a) β-eucryptite under a hydrostatic pressure of 3 GPa at 300 K. The amorphization proceeds via relative tilting of SiO4 (orange) and AlO4 (gray) [panel (b)] that eventually leads to change in O coordination around Al resulting in AlO3 (pink) and AlO5 polyhedra [panel (c)–(h)]. Significant disordering of Li (purple) is observed resulting in the formation of Li–O (blue) bonds. For the sake of clarity, computational supercell (outlined by black lines) is replicated along the three supercell vectors.
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