Comment on: Evidence and Stability Field of fcc Superionic Water Ice Using Static Compression

TL;DR

This paper critiques recent experimental claims about the stability fields of superionic water ice phases, emphasizing the challenges in accurately determining phase boundaries due to measurement difficulties.

Contribution

It challenges the reported phase boundaries of fcc superionic ice, highlighting experimental limitations and questioning the extended stability field claims.

Findings

Reported phase boundaries lack solid experimental justification

Measurement difficulties hinder accurate determination of phase stability

Critique of the extended stability field of fcc-SI ice

Abstract

Weck et al. (1) report on the existence and stability fields of two superionic (SI) phases of H2O ice at high P-T (P-T) conditions, which has been a topic of static and dynamic experiments and theoretical calculations (see Ref. (2) and references therein). They confirm Ref. (2) in that there are two SI phases with bcc and fcc oxygen sublattices with the stability at low- and high-P. However, they report on an extended stability field of fcc-SI ice toward lower T but no sign of it below 57 GPa. Here we argue that the reported phase boundaries of fcc-SI phase are not well experimentally justified due to difficulties to perform adequate X-ray diffraction (XRD) and radiometric measurements.