The complex kinetics of the ice VI to ice XV hydrogen ordering phase transition

TL;DR

This study investigates the complex, multi-stage hydrogen ordering transition from ice VI to ice XV using calorimetry, revealing challenges in achieving complete hydrogen order at ambient pressure due to kinetic limitations.

Contribution

It provides new experimental insights into the kinetics of ice VI to ice XV transition, highlighting the difficulty of fully hydrogen-ordering ice XV through simple cooling methods.

Findings

Fast hydrogen ordering occurs initially upon cooling.

A slower process leads to residual disorder in ice XV.

Complete hydrogen ordering is unlikely at ambient pressure.

Abstract

The reversible phase transition from hydrochloric-acid-doped ice VI to its hydrogen-ordered counterpart ice XV is followed using differential scanning calorimetry. Upon cooling at ambient pressure fast hydrogen ordering is observed at first followed by a slower process which manifests as a tail to the initial sharp exotherm. The residual hydrogen disorder in H2O and D2O ice XV is determined as a function of the cooling rate. We conclude that it will be difficult to obtain fully hydrogen-ordered ice XV by cooling at ambient pressure. Our new experimental findings are discussed in the context of recent computational work on ice XV.