Reversible first-order transition between two H2O amorphs at ∼0.2 GPa and ∼135 K

Abstract

Transition between the low‐ and high‐density amorphous H₂O was observed with a piston‐cylinder apparatus from 77 K to 140 K, almost the glass‐transition temperature of the amorphs. The transition was found to occur reversibly and abruptly at ∼135 K and ∼0.2 GPa with a volume change of 0.20±∼0.01 cm³/g and some hysteresis. This confirmed the transition to be first order. Absence of intermediate amorphous states between the low‐density and high‐density amorphs suggested existence of two substantially different liquid phases near the glass‐transition temperature.