TEMPERATURE-DEPENDENCE OF DIELECTRIC-RELAXATION IN H2O AND D2O ICE - A DISSIPATIVE QUANTUM TUNNELING APPROACH

We have measured the dielectric relaxation time of orientational defects for several 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 clearly identified, and experimental data have been successfully fitted with theoretical predictions. Particularly significant is the perfect agreement, near the crossover temperature T(c), of all our different samples with a universal scaling law, as predicted by DQT theory, and here experimentally verified for the first time. The crossover temperature T(c), where quantum tunneling and thermal hopping merge, has been found close to 240 and to 220 K for H2O and D2O ices, respectively, thus showing the higher relevance of quantum effects in H2O ice, as expected. It is shown that the dielectric relaxation time of orientational defects for both H2O and D2O ice samples never attains a fully classical behavior, even at their melting temperature. Implications of these findings for the mechanism of migration for orientational defects associated with impurities and water interstitials in ice physics are discussed.