Ice XV: a new thermodynamically stable phase of ice

TL;DR

This paper reports the discovery and structural determination of a new thermodynamically stable ice phase, ice XV, which is hydrogen-ordered, stable below 130 K in specific pressure ranges, and exhibits antiferroelectric properties.

Contribution

The paper identifies and characterizes ice XV as a new stable phase, providing its structure and stability conditions, and challenges previous theoretical predictions about its ferroelectric nature.

Findings

Ice XV is thermodynamically stable below 130 K in 0.8-1.5 GPa pressure range.

Ice XV has an antiferroelectric structure, contrary to some theoretical predictions.

The stability regions of hydrogen-ordered ice phases have been mapped.

Abstract

A new phase of ice, named ice XV, has been identified and its structure determined by neutron diffraction. Ice XV is the hydrogen-ordered counterpart of ice VI and is thermodynamically stable at temperatures below ~130 K in the 0.8 to 1.5 GPa pressure range. The regions of stability in the medium pressure range of the phase diagram have thus been finally mapped, with only hydrogen-ordered phases stable at 0 K. The ordered ice XV structure is antiferroelectric, in clear disagreement with recent theoretical calculations predicting ferroelectric ordering.