HOPPING AND DISSIPATIVE TUNNELING OF ORIENTATIONAL DEFECTS IN ICE

Abstract

We have measured the dielectric relaxation time of orientational defects for H2O and D2O polycrystalline ice samples, in the temperature range 200–270 K, and over the frequency range 0.3–1000 kHz. Results are in good agreement with previous studies, and at T<240 K departures from the familiar Arrhenius law have been observed. We show that these deviations from classical rate theory can be well described within the framework of dissipative quantum tunneling (DQT) theory, assuming impurity-generated Bjerrum defects responsible for the observed dielectric relaxation process over the entire temperature range investigated. The temperature regions where quantum tunneling, crossover to thermal hopping, and quantum corrections to classical laws, respectively prevail are here reviewed. Particularly significant is the perfect agreement, near the crossover temperature Tc, of all our different samples with a universal scaling law, as predicted by DQT theory. The crossover temperature Tc, where quantum tunneling and thermal hopping merge, has been found close to 240 K and to 220 K for H2O and D2O ice respectively, thus showing the higher relevance of quantum effects in H2O ice. It is shown that the dielectric relaxation time of orientational defects for both H2O and D2O ice samples never attains a fully classical behaviour, even at their melting temperature.