Water ice dissociates into a superionic solid at high temperature (>2,000K) and pressure, where oxygen forms the lattice, but hydrogen diffuses completely. At low temperature, however, the dissociation into an ionic ice of hydronium (H3O)+ hydroxide (OH)- is not expected because of the extremely high energy cost (-1.5eV) of proton transfer between H2O molecules. Here we show the pressure-induced formation of a partially ionic phase (monoclinic P21 structure) consisting of coupled alternate layers of (OH)δ- and (H3O) δ+ (δ =0.62) in water ice predicted by particle-swarm optimization structural search at zero temperature and pressures of >14 Mbar. The occurrence of this ionic phase follows the break-up of the typical O-H covalently bonded tetrahedrons in the hydrogen symmetric atomic phases and is originated from the volume reduction favourable for a denser structure packing.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)