High-density amorphous ice and its phase transition to ice XII

High-density amorphous ice, HDA, was heated in a pressure vessel with indium linings 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 N(2) at 1 bar. The metastable domain of ice XII thus revealed extends between approximate to 158-212 K from approximate to 0.7 to approximate to 1.5 GPa, and is in a different region of water's phase diagram than that shown by Koza et al. [Phys. Rev. Lett. 85, 334 (2000)]. When HDA, or hexagonal ice, is compressed without using indium linings, ice XII can form even when the pressure vessel is immersed in liquid N2, but it requires a pronounced apparent pressure drop at pressures greater than or equal toapproximate to 1.1 GPa. These apparent pressure drops can be caused by buildup of friction. We propose that shock-waves generated by apparent pressure drops cause transient local heating up to the temperature range of the ice XII metastable domain, and that this induces nucleation and crystal growth. Pressure-displacement curves obtained on compression of ice Ih axe consistent with formation of ice XII from HDA only, and not from ice Ih.