Ice IX: An Antiferroelectric Phase Related to Ice III

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Abstract
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 interaction increases the absorption frequencies. The high‐frequency dielectric constant decreases by about 5.7% at the III‐IX transition although there is little volume change; this decrease might be a valuable way of detecting order‐disorder transitions, particularly if they proceed slowly. The infrared polarizabilities of the various phases are briefly discussed. Ice IX could not be warmed into III because it always transforms to the more stable ice II.

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