A new high-pressure structure of SiO2directly converted from α-quartz under nonhydrostatic compression

Abstract

High-pressure behavior of SiO₂is one of the prototypical subjects in several research areas including condensed matter physics, inorganic chemistry, mineralogy, materials science, and crystallography. Therefore, numerous studies have been performed on the structure evolution of SiO₂under pressure. Here, we show a new structure directly converted fromα-quartz under uniaxial compression. Ourab initiocalculations elucidate a simple transition pathway fromα-quartz to the Fe₂P-type phase, and an intermediate state with the Li₂ZrF₆-type structure appears in this structure conversion. Some interesting properties are found on this intermediate state. (1) The Li₂ZrF₆-type phase is metastable probably due to a volumetric unbalance between the Li and Zr sites but becomes more energetically stable thanα-quartz over ∼12 GPa. (2) It is vibrationally stable at 0 GPa, suggesting that this phase can be recovered down to ambient condition once synthesized. (3) The crystal structures of Li₂ZrF₆-type SiO₂and phase D, one of dense magnesium hydrous silicates, are found identical, suggesting the stabilization of their solid solution under high-P,Tcondition.

Keywords: Li2ZrF6-type structure; SiO2; ab initio method; high-pressure; structure evolution.