The dielectric relaxation time of ice V, its partial anti-ferroelectric ordering and the role of Bjerrum defects

Abstract

The dielectric relaxation spectra of ice V has been studied over the 133–270 K range, at frequencies in the 0.05 Hz–300 kHz range. Its dielectric relaxation time, τ, is 1.5 s at 133 K. The Arrhenius plot of its τ is found to bend sharply at ∼200 K, and the Arrhenius energy decreases from 49.9 kJ/mol at 260 K to 23.3 kJ/mol at 160 K. This confirms the inference from the orientational ordering studies that τ of ice V at 125 K is much less than 100 s [J. Chem. Phys. 112, 7169 (2000)]. The increase in the equilibrium permittivity on cooling ice V from 266 to 133 K is 77% of that anticipated from a decrease in its volume and thermal energy. The discrepancy is attributed to a gradual increase in orientational ordering of water molecules in its structure, leading to a partially antiferroelectric state at low temperatures. A comparison made with the earlier studies of uncontaminated (H2O and D2O) ice Ih and N2- and CO2-contaminated (H2O) ice Ih (impurities in the latter used to generate extrinsic Bjerrum defects), showed that the decrease in the Arrhenius energy on cooling ice V may be explained without invoking a change in mechanism from Bjerrum defects diffusion to ionic defects diffusion with zero activation energy.