Decomposition and terapascal phases of water ice

TL;DR

This study predicts the decomposition of water ice into hydrogen peroxide and a hydrogen-rich phase at around 5 TPa, along with new stable ice phases at high pressures, and discusses implications for planetary cores.

Contribution

The paper introduces new high-pressure phases of water ice and predicts decomposition pathways and metallization pressures using computational methods.

Findings

H2O decomposes into H2O2 and hydrogen-rich phases above 5 TPa.

New stable water ice phases are identified between 0.8 and 2 TPa.

H2O metallization occurs above 6 TPa, with no stable metallic form at low temperatures.

Abstract

Computational searches for stable and metastable structures of water ice and other H:O compositions at TPa pressures have led us to predict that H$_2$O decomposes into H$_2$O$_2$ and a hydrogen-rich phase at pressures of a little over 5 TPa. The hydrogen-rich phase is stable over a wide range of hydrogen contents, and it might play a role in the erosion of the icy component of the cores of gas giants as H$_2$O comes into contact with hydrogen. Metallization of H$_2$O is predicted at a higher pressure of just over 6 TPa, and therefore H$_2$O does not have a thermodynamically stable low-temperature metallic form. We have also found a new and rich mineralogy of complicated water ice phases which are more stable in the pressure range 0.8--2 TPa than any predicted previously.