title: High pressure partially ionic phase of water ice.
abstract: Water ice dissociates into a superionic solid at high temperature (>2,000 K) and pressure, where oxygen forms the lattice, but hydrogen diffuses completely. At low temperature, however, the dissociation into an ionic ice of hydronium (H(3)O)(+) hydroxide (OH)(-) is not expected because of the extremely high energy cost (~1.5 eV) of proton transfer between H(2)O molecules. Here we show the pressure-induced formation of a partially ionic phase (monoclinic P2(1) structure) consisting of coupled alternate layers of (OH)(δ-) and (H(3)O)(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.
authors: State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China.
authors: Yanchao
authors: Y
authors: Wang
authors: Hanyu
authors: H
authors: Liu
authors: Jian
authors: J
authors: Lv
authors: Li
authors: L
authors: Zhu
authors: Hui
authors: H
authors: Wang
authors: Yanming
authors: Y
authors: Ma
mesh_terms: D007053:Ice; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D007053:Ice; D014867:Water