Dielectric properties of polycrystalline D 2 O ice Ih (hexagonal)

Abstract

Measurements of the dielectric permittivity and loss of polycrystalline 98.75% D 2 O ice Ih have been made in the temperature range 77-274 K and in the frequency range 10 -2 to 5 x 10 7 Hz. In addition, isothermal decay of stored charge has been measured by a transient current method. The orientation polarization in D 2 O ice is found to be the sum of the contri­butions from three relaxation processes, each being of the Debye-type, with the fastest one nearly two orders of magnitude smaller than the other two. The individual contribution of these processes to the orientation polarization, and their respective relaxation times, vary with temperature in such a manner as to increase the width of the absorption spectrum with decreasing temperature. The magnitude of the equilibrium dielectric permittivity obeys the Curie-Weiss law with T c = 27 K. The equilibrium dielectric permittivity of D 2 O ice is about 7% higher than that of H 2 O ice. This effect is similar to that seen in many hydrogen bonded solids in the paraelectric state and may indicate a 4% higher effective dipole moment in D 2 O than in H 2 O ice. The high frequency permittivity of D 2 O ice is 4-5% lower than that of H 2 O ice. The difference is partly due to the lower optical polarizability of the D 2 O molecule but is mainly due to the difference in the absorption of infrared frequencies. The (∂ є ∞ /∂ T ) p decreases with temperature. The relaxation in D 2 O ice is 40% slower than in H 2 O ice near 260 K. An Eyring plot of the average relaxation time gives an activation energy of 50.0 kJ mol -1 at temperatures above 250 K. With decreasing temperature the activation energy first decreases until about 170 K and then begins to increase slowly. The decrease in the activation energy is likely caused by a change in the magnitude of the roles of intrinsic orientational defects associated with the ideal ice lattice, and extrinsic orientational defects introduced by impurities, grain boundaries, etc., in determining the molecular re-orientation rates. The increase in the activation energy at temperature below 170K is probably due to the concerted motion of the water molecules. The Arrhenius plot of the high-frequency conductivity is similar to that of the reciprocal average relaxation time. It is shown that the high frequency conductivity is determined largely by the same mechanism as is responsible for dielectric relaxation.