Room temperature electrofreezing of water yields a missing dense ice phase in the phase diagram

Weiduo Zhu,Lan-Feng Yuan,Jijun Zhao,Jinlong Yang,Hong-Hui Wu,Joseph S Francisco,Chongqin Zhu,Lu Wang,Xiao Cheng Zeng,Jaeil Bai,Yingying Huang

doi:10.1038/s41467-019-09950-z

Abstract

Water can freeze into diverse ice polymorphs depending on the external conditions such as temperature (T) and pressure (P). Herein, molecular dynamics simulations show evidence of a high-density orthorhombic phase, termed ice χ, forming spontaneously from liquid water at room temperature under high-pressure and high external electric field. Using free-energy computations based on the Einstein molecule approach, we show that ice χ is an additional phase introduced to the state-of-the-art T–P phase diagram. The χ phase is the most stable structure in the high-pressure/low-temperature region, located between ice II and ice VI, and next to ice V exhibiting two triple points at 6.06 kbar/131.23 K and 9.45 kbar/144.24 K, respectively. A possible explanation for the missing ice phase in the T–P phase diagram is that ice χ is a rare polarized ferroelectric phase, whose nucleation/growth occurs only under very high electric fields.

Highlights

Water can freeze into diverse ice polymorphs depending on the external conditions such as temperature (T) and pressure (P)
We report the formation of a previously unreported ice structure, termed ice χ, which can be observed to form spontaneously in the molecular dynamics (MD) simulation of liquid water at room temperature and under an electric field below the threshold strength
Our ab initio MD simulations show that dissociation of water molecule can be clearly seen, within 1 ps simulation time, in bulk liquid water at 270 K and 10.0 V nm−1, dissociation of water was not observed within 5 ps simulation time for the liquid water at 270 K and 5.0 V nm−1; such an event would be very unlikely to occur when the water was under the electric field

Summary

Introduction

Water can freeze into diverse ice polymorphs depending on the external conditions such as temperature (T) and pressure (P). Molecular dynamics simulations show evidence of a high-density orthorhombic phase, termed ice χ, forming spontaneously from liquid water at room temperature under high-pressure and high external electric field. Hu et al.[38] provided simulation details on the behaviour of glassy water in external electric fields, including the formation of a body-centred-cubic (bcc) ice phase at 77 K This bcc ice phase is polarized ferroelectric ice VIII, as determined by its lattice constant of 3.19 ± 0.17 Å and oxygen–oxygen (O–O) radial distribution function (RDF)[43,44]. We report the formation of a previously unreported ice structure, termed ice χ, which can be observed to form spontaneously in the MD simulation of liquid water at room temperature and under an electric field below the threshold strength. The electric-field-induced crystallization of liquid water may serve as an alternative approach to attain new phase structures of water, the ferroelectric ices

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Results

Conclusion