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- Johari, G P, et al.
(author)
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In situ transformation of amorphous ices at high pressures
- 2007
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In: Physical Review B. ; 76, s. 134103-1
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Journal article (peer-reviewed)abstract
- By using thermal conductivity and its change with temperature and pressure as a criteria for in situ structural transformation of the crystalline and amorphous solid forms of water, we report two findings: (i) transformation of high-density amorph (HDA) directly to cubic ice on slow depressurization and (ii) slow transformation or dilation of metastable HDA at 130 K to a low-density amorph (LDA) even when the pressure was increased from 0.2 to 0.3 GPa, and then gradual reversion by collapse of the LDA to HDA on further pressurization to 0.5 GPa. We also discuss implications of these findings for the current understanding of the transformations of metastable ices under pressure, particularly of those studied in situ.
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- Johari, G.P., et al.
(author)
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Vibrational and relaxational properties of crystalline and amorphous ices
- 2007
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In: Thermochimica Acta 461, issue 1-2. - : Elsevier BV. ; , s. 14-43
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Conference paper (peer-reviewed)abstract
- Pure water forms 15 crystalline ices at different temperatures and pressures, and its solutions containing small molecules form three crystallographically distinct clathrates. Its vapours deposited on a substrate at T< 100K produce a porous amorphous solid and pure water vitrifies (T-g = 136 K) when hyperquenched in micron-size droplets. At a temperature below 140 K, hexagonal and cubic ice collapse when pressure exceeds similar to 1 GPa to a similar to 30% denser amorphous solid, which on heating at ambient pressure transforms to an amorphous solid with density similar to that of hexagonal ice. In this essay, we describe (i) the thermal conductivity of the ices and clathrates and the thermal conductivity and heat capacity of water's amorphous solids, their thermodynamic paths and their transformations, and (ii) the dielectric relaxation time of ultraviscous water formed on heating the amorphous solids. We also describe the characteristics of pressure collapse and subsequent amorphization of hexagonal and cubic ices that occurs over a period of several days according to a stretched exponential kinetics and a pressure-, and temperature-dependent rate constant. This process is attributed to the production of lattice faults during deformation of the ice and the consequent distribution of the Born instability pressures. This ultimately produces a kinetically unstable high-energy amorphs in the same manner as random deformation of crystals produces kinetically unstable high-energy amorphs, with density and properties depending upon their temperature-pressure-time history. On heating at 1 GPa pressure, the pressure-amorphized solid relaxes to a lower energy state, becoming ultraviscous water at 140 K. But on heating at ambient pressure, it irreversibly transforms slowly to a low-density amorph that differs from glassy water and vapour-deposited amorphous solid.
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