Tests for thermodynamic state of water's high-density amorph.

Analysis of the density and ultrasonic velocity data for water's high-density amorph (HDA) far from its formation conditions shows that HDA made by pressurizing ice Ih is different from HDA made by pressurizing its low-density amorph (LDA), and the density and ultrasonic velocity of HDA depend upon the pressure and temperature path used to make it from ice Ih. This seems inconsistent with the description of HDA-LDA phase equilibrium. Similar tests may be used to clarify the nature of the nonergodic transitions in GeO(2) and SiO(2).