D. W. Davidson

Ice IX: An Antiferroelectric Phase Related to Ice III

The dielectric properties of ice III in the frequency range 10−1 to 105 cps have been measured down to − 160°C. There is a gradual transition from the orientationally disordered III to an orientationally ordered and probably antiferroelectric phase, which is designated IX, starting at about − 65°C and reaching completion at about − 108°C. An arrangement of the hydrogen atoms in ice IX is proposed. The amplitude of the orientational polarization decreases continuously through the transformation region although the relaxation time is close to the value extrapolated from previous measurements in the disordered phase. The limiting high‐frequency dielectric constant of the dispersion decreases with decreasing temperature. The cause of this behavior, which is unusual for molecular crystals, is undoubtedly that the polarization of the lattice vibrations contributes a large part of the high‐frequency dielectric constant. This contribution decreases with decreasing temperature because the decreasing anharmonic int...

Dielectric Properties of Ices II, III, V, and VI

The dielectric properties of Ices II, III, V, and VI have been measured up to 300 kc/sec over a range of temperatures and pressures. All except Ice II exhibited well‐defined dielectric dispersion and so are orientationally disordered under the experimental conditions. The dispersion loci were slightly broader than Debye curves, which may reflect the presence of nonequivalent crystal sites. As for Ice I, the static dielectric constants correspond to values of about 3 for the Kirkwood orientational correlation factor. This suggests that these forms of ice are four coordinated, in agreement with infrared and (for Ice III) x‐ray evidence at low temperatures. The relaxation rates are considerably faster than for Ice I, and the activation energies and entropies somewhat lower. The volumes of activation are all about 4.6 cm3 mole−1. The relaxation mechanism appears to be similar to that in Ice I, i.e., relaxation occurs by diffusion of orientational defects.X‐ray and infrared studies have indicated that Ice II i...

Dielectric Behavior of Cubic and Hexagonal Ices at Low Temperatures

Cubic ice Ic and hexagonal ice Ih were prepared in pressurizable dielectric cells at temperatures near − 110°C from the high‐pressure ices II and IX. No differences were found between the dielectric properties of Ic and Ih. Freshly prepared samples exhibited longer relaxation times at low temperatures than those commonly found for samples of Ih prepared directly by freezing purified water. These long relaxation times became appreciably shorter with sample aging. These results are attributed to precipitation of impurities from ices II and IX, followed by their gradual reincorporation in the ice I lattice. At temperatures as high as − 50°C the isothermal sequence of transformations I→II→I is capable of producing a substantial degree of purification of ice I in terms of its dielectric relaxation time.

Dielectric Properties of Ice VII. Ice VIII: A New Phase of Ice

The dielectric properties of ice have been studied up to 107 kbar using opposed circular anvils. Ice VII undergoes orientational polarization, and consequently its molecules are orientationally disordered. The volume of activation for the relaxation of the orientational polarization is ∼3 cm3 mole−1, which suggests that the reorientation occurs by the migration of Bjerrum defects, as it appears to do in ice I, III, V, and VI. The energy and entropy of activation at 23 kbar are about 11.6 kcal mole−1 and 9.2 cal deg−1·mole−1, which are similar to those for other phases of ice.At about 0°C, ice VII undergoes a transformation to a phase, here designated ice VIII, whose molecules are orientationally immobile at audio frequencies. This phase had previously been suggested by an analysis of the boundary line between ice VI and VII. The transformation occurs with a hysteresis of about 5.5°C at constant pressure, and the transformation temperature is independent of pressure to within about 0.5° up to 50 kbar. Some...

Effect of Pressure on the Dielectric Properties of Ice I

The effect of pressure up to about 2 kbar on the dielectric properties of Ice I at − 23.4° has been measured. The static dielectric constant increases with increasing pressure by about the amount predicted by the Kirkwood theory. The increase in relaxation time yields a volume of activation for the relaxation process of 2.9±0.2 cm3 mole−1 which supports current views that dielectric relaxation occurs by rotation at orientational defects. The volume of activation given by the rapid rise of dc conductivity with increasing pressure is − 11±∼3 cm3 mole−1 which is consistent with the proton‐transfer mechanism.

Dielectric Study of Some Liquid Alkyl Nitrites

The dielectric constants of liquid methyl, n‐propyl and isopropyl nitrite have been measured over an extensive range of temperature and the results used to estimate the relative abundances of the trans and cis isomers. It is concluded that the trans form predominates in all three liquids, in contradiction, in the case of the propyl nitrites, to the conclusions from recent NMR studies. It is suggested that the assignments to the appropriate NMR peaks should be reversed for the higher alkyl nitrites. Dielectric relaxation in n‐propyl nitrite was found to be of the asymmetrical Cole‐Davidson type.

Proton Resonance Spectra of Some Gas Hydrates

Proton resonance spectra have been obtained for a variety of clathrate hydrates as a function of temperature from near the decomposition point to about −70°C. It is possible to calculate the Arrhenius activation energy (∼8 kcal mole−1) for motional narrowing of the linewidths of the host molecules and this is attributed to the combined effects of rotation and diffusion in the solid. By selective deuteration linewidths are found for proton‐containing guest molecules. The guest molecules undergo rapid rotation in the solid.