Dielectric properties of high-density amorphous ice under pressure

The dielectric properties of high density amorphous ice, which is produced by slow isothermal pressurization (similar to 0.1 GPa h(-1)) at 130 K, have been studied by dielectric spectroscopy, in situ, at pressures up to 1.2 GPa and temperatures from 130-160 K. The dielectric relaxation time tau is about 5 s at 130 K and follows an Arrhenius temperature dependence with an activation energy E-a=45 kJ mol(-1) at 1 GPa. The short tau indicates that the amorph at 1 GPa is an ultraviscous liquid well before it crystallizes at similar to 160 K. The equilibrium permittivity is similar to 157 at 138 K and 1 GPa, which yields a Kirkwood correlation factor g(K) of only 1.7, indicating a much smaller dipolar orientational correlation than that of the stable crystalline phase ice VI (g(K)=3.4) and liquid water at atmospheric pressure (g(K)=2.9 at 273 K). The activation volume is 1.7 cm(3) mol(-1) in the pressure range 0.45 to 1.15 GPa at 130 K which, together with E-a, yields a weak pressure dependence of the glass transition temperature T-g of dT(g)/dp=5 K GPa(-1).