Hexagonal ice transforms at high pressures and compression rates directly into “doubly metastable” ice phases

Abstract

We report compression and decompression experiments of hexagonal ice in a piston cylinder setup in the temperature range of 170-220 K up to pressures of 1.6 GPa. The main focus is on establishing the effect that an increase in compression rate up to 4000 MPa/min has on the phase changes incurred at high pressures. While at low compression rates, a phase change to stable ice II takes place (in agreement with earlier comprehensive studies), we find that at higher compression rates, increasing fractions and even pure ice III forms from hexagonal ice. We show that the critical compression rate, above which mainly the metastable ice III polymorph is produced, decreases by a factor of 30 when decreasing the temperature from 220 to 170 K. At the highest rate capable with our equipment, we even find formation of an ice V fraction in the mixture, which is metastable with respect to ice II and also metastable with respect to ice III. This indicates that at increasing compression rates, progressively more metastable phases of ice grow from hexagonal ice. Since ices II, III, and V differ very much in, e.g., strength and rheological properties, we have prepared solids of very different mechanical properties just by variation in compression rate. In addition, these metastable phases have stability regions in the phase diagrams only at much higher pressures and temperatures. Therefore, we anticipate that the method of isothermal compression at low temperatures and high compression rates is a tool for the academic and industrial polymorph search with great potential.

Temperature-induced amorphisation of hexagonal ice

“…Ice IV is known to crystallise from amorphous ice at high-pressure conditions, [39][40][41] but has never been observed to crystallise from hexagonal ice or any other ice polymorph. By contrast, ice IX/III may crystallise from hexagonal ice or from ice V. [42][43][44][45][46] The amorphous halo peak, also called first sharp diffraction peak by some, 47 is found at 2y = 32.51 (see dotted grey line in Fig. 2), which corresponds to the position found in very high-density amorphous ice (VHDA).…”

Shrinking water's no man's land by lifting its low-temperature boundary

“…the discussion in [68]). Bulk ice I h can be overpressurized [71], and thus a (metastable equilibrium) phase boundary with metastable ice IX exists, as shown in water's phase diagram in Fig. 4.…”

Relaxation Time of High-Density Amorphous Ice

“…LDA transition temperature, observed in ex situ differential scanning calorimetry experiments, which is a novel approach developed in our group [21]. The suitability of ex situ characterization, the so-called quench recovery procedure, is documented elsewhere [26]. Using this approach we extract alpha relaxation times of HDA at 0.1 and 0.2 GPa.…”