Pressure-Induced Amorphization and Phase Transformations in β-LiAlSiO₄

Τhis work presents a comprehensive study on pressure-induced amorphization (PIA) in β-eucryptite (LiAlSiO 4 ) and on the equilibrium states of so-formed amorphous phase at elevated temperatures. Our results revealed that at 300 K β-LiAlSiO 4 underwent progressive amorphization at pressures above 4.5 GPa and became completely amorphous above 17.0 GPa. After release of pressure, β-LiAlSiO 4 that was partially amorphized at 7.5, 14.0, and 16.0 GPa reverted back to its original crystalline state. When subjected to a complete loss of long-range structural order, the system was recovered as an amorphous state and did not retain the so-called structural memory. Upon heating at high pressures, the partially or completely amorphous β-LiAlSiO 4 transformed into various crystalline phases at temperatures above 973 K: between 6.9 and 10.7 GPa it was decomposed into a mixture of LiAlSi 2 O 6 and LiAlO 2; at 15.3 GPa the two phases recombined to form a new phase with a spinel structure; and at 22 GPa the spinel phase of LiAlSiO 4 was decomposed into its constituent oxides. The observed transformations are all of a reconstructive type and also involve profound changes in atomic coordination environments. A large activation energy barrier associated with coordination changes and a hindrance of atomic mobility at kinetically low temperatures are the primary factors that trigger the PIA.