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. 3em{0ex}GPa0. 3em{0ex}h^-1) at 1300. 3em{0ex}K, have been studied by dielectric spectroscopy, in situ, at pressures up to 1. 20. 3em{0ex}GPa and temperatures from 130--1600. 3em{0ex}K. The dielectric relaxation time is about 50. 3em{0ex}s at 1300. 3em{0ex}K and follows an Arrhenius temperature dependence with an activation energy E₀=450. 3em{0ex}kJ0. 2em{0ex}mol^-1 at 10. 3em{0ex}GPa. The short indicates that the amorph at 10. 3em{0ex}GPa is an ultraviscous liquid well before it crystallizes at 1600. 3em{0ex}K. The equilibrium permittivity is 157 at 1380. 3em{0ex}K and 10. 3em{0ex}GPa, which yields a Kirkwood correlation factor g₊ of only 1. 7, indicating a much smaller dipolar orientational correlation than that of the stable crystalline phase ice VI (g₊=3. 4) and liquid water at atmospheric pressure (g₊=2. 9 at 2730. 3em{0ex}K). The activation volume is 1. 70. 3em{0ex}cm^30. 2em{0ex}mol^-1 in the pressure range 0. 45 to 1. 150. 3em{0ex}GPa at 1300. 3em{0ex}K which, together with E₀, yields a weak pressure dependence of the glass transition temperature T₆ of dT₆∕dp=50. 3em{0ex}K0. 2em{0ex}GPa^-1.