Crossover between the Thermodynamic and Nonequilibrium Scenarios of Structural Transformations of H_2O Ih Ice during Compression

摘要

A Detailed investigation of different scenarios of structural transformations of H_2O Ih ice during compression to a pressure of 2 GPa in the temperature range from 77 to 200 K is performed. In the range of temperatures and pressures being treated, detailed data are obtained for the density and the shear modulus for different phases of ice including the hda, IX, and XII phases. The experimentally obtained correlations for the density and ultrasonic velocities, with due regard for the available data of structural investigations, are used to identify the transformation sequences Ih → hda (below 135 K), Ih → II → VI (above 165 K), and Ih → IX → VI (from 155 to 180 K). In the vicinity of the crystallization temperature of amorphous ice, i.e., at about 140 K, an anomalous transformation pattern is observed, which is interpreted as predominantly the Ih → XII phase transition. The temperature crossover is discussed between the mode of solid-phase amorphization (Ih → hda) and crystal-crystal transitions, as well as the metastable nature of IX ice and the mechanism of solid-phase amorphization.