Most experimentally known high-pressure ice phases have a body-centred cubic (bcc) oxygen lattice. Our atomistic simulations show that, amongst these bcc ice phases, ices VII, VII' and X are the same thermodynamic phase under different conditions, whereas superionic ice VII'' has a first-order phase boundary with ice VII'. Moreover, at about 300 GPa, ice X transforms into the Pbcm phase with a sharp structural change but no apparent activation barrier, whilst at higher pressures the barrier gradually increases. Our study thus clarifies the phase behaviour of the high-pressure insulating ices and reveals peculiar solid-solid transition mechanisms not known in other systems.
@article{arxiv.2203.12897,
title = {Same and interconvertible high-pressure ice phases},
author = {Aleks Reinhardt and Mandy Bethkenhagen and Federica Coppari and Marius Millot and Sebastien Hamel and Bingqing Cheng},
journal= {arXiv preprint arXiv:2203.12897},
year = {2022}
}