Ultrasonic study of the nonequilibrium pressure-temperature diagram of H2O ice -: art. no. 094205

We present a detailed ultrasonic study of the low-temperature nonequilibrium (transitional) phase diagram of H2O ice in the pressure range 0-1.7 GPa and temperature range 77-200 K. A continuous crossover from the thermodynamically driven Ih-II transition to the nonequilibrium scenario of solid-state amorphization Ih-hda through the intermediate I-IX transition was clearly observed for pressurized ice Ih at the temperature decrease. The Ih-IX transition was detected by the abrupt shift of the IX-VI transition toward lower pressures with respect to the II-VI transition in accordance with the thermodynamic trend. The anomalous picture of transformation at 140 K (near the crystallization temperature of amorphous ices) was interpreted as basically the Ih-XII transition. Elastic softening was established to be the common precursor for the solid-state amorphization Ih-hda and transformation between the Ida and hda amorphous phases of ice. The mechanism of amorphization is discussed in terms of lattice instability. Three distinct stages (shear elastic softening, bulk softening, and main volume jump) were found for the temperature-induced hda-Ida transformation. Similarity in elastic softening of the pressurized Ih lattice and Ida network clarifies the differences in the structural and dynamic nature of Ida and hda ices. The detailed picture of amorphous-amorphous transformations shows their complicated nonergodic nature combining the features typical for both the first-order transition and singularity-free scenario.