Dielectric Relaxation in Ice and Ice Clathrates and Its Connection to the Low-Temperature Phase Transition Induced by Alkali Hydroxides as Dopants

Abstract

We have used dielectric spectroscopy (frequency range 106 to 10-3.0 Hz) and differential scanning calorimetry down to a temperature of 77 K to study the effect of alkali hydroxides as dopants on the molecular relaxation in hexagonal ice (Ih) and in clathrate hydrates (Ic) of acetone and 1,4-dioxane. A drastic fall in the relaxation times of the order of 107−1012 has been noticed in Ih and Ic doped with alkali hydroxides, namely, KOH, NaOH, LiOH, and Ca(OH)2. It appears that the alkali metal- and hydroxyl-ion pairs exert a large influence on the orientational mobility of water molecules by way of polarization over a domain, and the pure phase of Ih (or Ic) is maintained outside the domains thus leading to orientational heterogeneity in the samples. The amount of phase that gets transformed to the low-temperature (low-T) ordered phase depends on the solid solubility of the dopant. The nature of the relaxation and variation of the static dielectric constant have been examined critically to get an insight int...