Atomic-scale mechanism for pressure-induced amorphization of β-eucryptite

Abstract

We present here a reactive force field based metadynamics study of pressure-induced amorphization in β-eucryptite, a lithium aluminum silicate that exhibits negative thermal expansion, i.e., volumetric contraction upon heating. From our simulations, we found that β-eucryptite amorphizes under a moderate applied pressure of ∼3 GPa. A careful inspection of the amorphous phase showed that it contains AlO3, AlO4, AlO5, and SiO4 polyhedra, indicating clear short-range order. We have also identified the atomic-scale processes responsible for the amorphization of β-eucryptite. These processes are (a) tilting and distortion of tetrahedra centered at Al/Si, (b) change in atomic coordination around Al, and (c) disordering of Li atoms with the formation of Li-Li, Li-O, and Li-O-Li linkages. We discuss our results in the context of a possible general link between negative thermal expansion, radiation tolerance, and pressure-induced amorphization in flexible network structures.