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Abstract
A theory of the anelastic relaxation in orientationally disordered cubic and hexagonal ice crystals is presented. The relaxation is due to the redistribution of water molecules among different orientations allowed by the Bernal-Fowler rules. The part of the free energy which depends on the protonic configuration is small and may be described as a sum of the elastic dipole interactions of individual molecules with the crystalline medium. Nowick and Heller's (1965) theory of the relaxation of crystals containing point defects is generalized in order to take into account the correlations of the orientations of neighbouring molecules. Because of the correlation the relaxation of elastic constants for strains F 2 in ice I c and strains A 1in ice I h is zero in the linear graph approximation. The correlation is important in all cases except for the relaxation due to strains E in ice I c. The correlation prevents the detection of the asymmetry of the elastic dipoles. A simple microscopic description of the elastic dipole, based on the valence force model, is presented. The relation to the Bass (1958) theory of relaxation is discussed.