(Meta-)stability domain of ice XII revealed between ≈158–212 K and ≈0.7–1.5 GPa on isobaric heating of high-density amorphous ice

High-density amorphous ice was heated at constant pressures of between 0.52 to 1.9 GPa from 77 K up to 240 K. The formed phases were characterized by x-ray diffractograms of samples recovered under liquid N2 at 1 bar. The (meta)stability domain of ice XII thus revealed extends between ≈158–212 K from ≈0.7 to ≈1.5 GPa. We further discuss whether ice XII has a low-temperature region of stability within the ice VI domain. Our (meta)stability domain of ice XII is in a different region of water’s phase diagram than that shown by Koza et al. [Phys. Rev. Lett. 84, 4112 (2000)].