Prediction of new thermodynamically stable aluminum oxides

TL;DR

This study predicts the formation of two new thermodynamically stable aluminum oxides, Al4O7 and AlO2, under high pressure, revealing their unique structures and electronic properties, expanding understanding of aluminum oxide chemistry.

Contribution

The paper introduces the discovery of two novel stable aluminum oxide compounds, Al4O7 and AlO2, using structure prediction algorithms under high-pressure conditions.

Findings

Al4O7 and AlO2 are stable at high pressures (330-443 GPa).

Both compounds contain oxide and peroxide ions.

They are insulating with reduced band gaps due to peroxo groups.

Abstract

Recently, it has been shown that under pressure, unexpected and counterintuitive chemical compounds become stable. Laser shock experiments (A. Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition of alumina with the formation of free Al and a mysterious transparent phase. Inspired by these observations, with have explored the possibility of the formation of new chemical compounds in the system Al-O. Using the variable-composition structure prediction algorithm USPEX, in addition to the well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to be thermodynamically stable in the pressure range 330-443 GPa and above 332 GPa, respectively. Both of these compounds at the same time contain oxide O2- and peroxide O22- ions, and both are insulating. Peroxo-groups are responsible for gap states, which significantly reduce the electronic band gap of both Al4O7 and AlO2.