Volumetric study consistent with a glass-to-liquid transition in amorphous ices under pressure

Abstract

Dilatometry experiments on low- and high-density amorphous ices up to 0.30 GPa are presented together with powder x-ray diffraction data. Repeated isobaric heating and cooling cycles reveal three competing processes: irreversible (micro)structural relaxation, reversible relaxation, and (irreversible) crystallization. The third and subsequent heating runs produce identical curves, i.e., irreversible relaxation is absent. We interpret the deviation from linear expansivity in these curves as the onset temperature of the volumetric glass-to-liquid transition (${T}_{g, \mathrm{onset}}$) and report its dependence on pressure.