High-temperature and high-pressure plastic phase of ice at the boundary of liquid water and ice VII

Abstract

Simultaneous high-temperature and high-pressure studies reveal phase transformation of bulk liquid water to an ice-VII-like structure having an eight coordination. It was demonstrated through this numerical study that the observed high-temperature and high-pressure phase of water obtained upon shock compression and equilibration has high rotational diffusion and thereby the hydrogen dynamics of these crystal structures are significantly complex compared with ice VII. The current work provides new characterization methods for the numerically observed plastic crystal phase of ice at the boundary of the liquid water and ice VII phases in which the molecules have a defined lattice position but rotate freely. It is anticipated that the present work will provide important data and guide new theoretical and experimental investigations in the search for plastic crystal phases of water. The power spectra plots of bulk liquid water subjected to different temperature and pressure conditions have also been presented in this numerical study, demonstrating significant differences between these high-temperature and high-pressure shock-equilibrated phases and those of pure ice VII at 10 GPa and liquid water at ambient temperature and pressure, as well as at elevated pressures and temperatures.

Close-Packed Ices in Nanopores

“…Therefore, ice nanotubes [(4, 0) 3 ], [(3, 2) 3 ], and [(4, 1) 3 ] may be classified as plastic solids. The existence of plastic phases in bulk water has been predicted by computer simulations with a variety of water models. − ,− As we will see below, plastic ice forms are ubiquitous in cylindrical pores with varying diameters.…”

Temperature- and pressure-dependence of the hydrogen bond network in plastic ice VII

“…To locate the domain of existence of the plastic phase reported in fig. 1, we have followed previous investigations and combined information about the radial distribution function computed between oxygen atoms, g OO (r), the mean square displacement of oxygen atoms, the rotational autocorrelation function evaluated on the intramolecular O-H bonds, and the angular distribution of the polar angles θ for the O-H vectors [37][38][39][40][41][42][43][44][45][46][47][48] . In this article, we will not discuss them, rather we will focus on the HBN, reported in fig.…”

“…Numerical simulations place superionic ice VII at the boundaries of ice VII and liquid water above 20 GPa and 2000 K 32,[35][36][37] . Nonetheless, both classical and ab initio simulations have predicted that, at lower pressure and temperature, the boundary between ice VII and liquid water is a plastic phase 32,[37][38][39][40][41][42][43][44][45][46][47][48] (fig. 1).…”

“…Computer simulations have widely investigated the structural and dynamical properties of plastic ices [37][38][39][40][41][42][43][44][45][46][47][48] , but no focus has been devoted to the HBN and its topology. Considering the relevance of high pressure crystalline phases endowed with hydrogen mobility in ex-Accepted to J. Chem.…”

Electrolyte Permeability in Plastic Ice VII

“…On the other hand, ice VII is permeable to salt impurities that cause an increase of both the bulk modulus and of the density. − Nothing is known, and this is the subject of our work, about the interactions of electrolytes with plastic ice VII. Plasticity in water has been widely explored computationally in the context of ice VII − and has also been proposed to exist in ammonia, , while it has been recently obtained in a water/ammonia mixture . In plastic ice VII, water molecules are free rotors while the oxygen atoms sit in the ice VII lattice positions corresponding to a body-centered cubic (bcc) structure with Pn3m space group and two atoms per unit cell.…”