Ultrasonic study of the nonequilibrium pressure-temperature diagram of H2Oice - art. no. 094205

We present a detailed ultrasonic study of the low-temperature nonequilibriu m (transitional) phase diagram of H2O ice in the pressure range 0-1.7 GPa a nd temperature range 77-200 K. A continuous crossover from the thermodynami cally 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 tran sition was detected by the abrupt shift of the IX-VI transition toward lowe r pressures with respect to the II-VI transition in accordance with the the rmodynamic trend. The anomalous picture of transformation at 140 K (near th e crystallization temperature of amorphous ices) was interpreted as basical ly the Ih-XII transition. Elastic softening was established to be the commo n precursor for the solid-state amorphization Ih-hda and transformation bet ween the Ida and hda amorphous phases of ice. The mechanism of amorphizatio n is discussed in terms of lattice instability. Three distinct stages (shea r elastic softening, bulk softening, and main volume jump) were found for t he temperature-induced hda-Ida transformation. Similarity in elastic soften ing of the pressurized Ih lattice and Ida network clarifies the differences in the structural and dynamic nature of Ida and hda ices. The detailed pic ture of amorphous-amorphous transformations shows their complicated nonergo dic nature combining the features typical for both the first-order transiti on and singularity-free scenario.