Dielectric properties of high-density amorphous ice under pressure

The dielectric properties of high density amorphous ice, which is produced by slow isothermal pressurization (~0.10.3em0exGPa0.3em0exh^-1) at 1300.3em0exK, have been studied by dielectric spectroscopy, in situ, at pressures up to 1.20.3em0exGPa and temperatures from 130--1600.3em0exK. The dielectric relaxation time τ is about 50.3em0exs at 1300.3em0exK and follows an Arrhenius temperature dependence with an activation energy Eₐ=450.3em0exkJ0.2em0exmol^-1 at 10.3em0exGPa. The short τ indicates that the amorph at 10.3em0exGPa is an ultraviscous liquid well before it crystallizes at ~1600.3em0exK. The equilibrium permittivity is ~157 at 1380.3em0exK and 10.3em0exGPa, which yields a Kirkwood correlation factor gK of only 1.7, indicating a much smaller dipolar orientational correlation than that of the stable crystalline phase ice VI (gK=3.4) and liquid water at atmospheric pressure (gK=2.9 at 2730.3em0exK). The activation volume is 1.70.3em0excm³0.2em0exmol^-1 in the pressure range 0.45 to 1.150.3em0exGPa at 1300.3em0exK which, together with Eₐ, yields a weak pressure dependence of the glass transition temperature Tg of dTg∕dp=50.3em0exK0.2em0exGPa^-1.