A new high-pressure structure of SiO2 directly converted from α-quartz under nonhydrostatic compression

High-pressure behavior of SiO2 is 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 SiO2 under pressure. Here, we show a new structure directly converted from alpha-quartz under uniaxial compression. Our ab initio calculations elucidate a simple transition pathway from alpha-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 than alpha-quartz over similar to 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 SiO2 and phase D, one of dense magnesium hydrous silicates, are found identical, suggesting the stabilization of their solid solution under high-P, T condition.

Automated summary

The high-pressure behavior of SiO2 is a key subject in various research areas. Researchers have shown a new structure directly converted from alpha-quartz under uniaxial compression and elucidated a simple transition pathway to the Fe2P-type phase. An intermediate state with the Li2ZrF6-type structure has been discovered, with some interesting properties. The Li2ZrF6-type phase is found to be metastable at lower pressures but becomes energetically stable than alpha-quartz at around 12 GPa, suggesting potential applications in ambient conditions.