Anisotopy of migration and faceting of large-angle grain boundaries in ice bicrystals

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Abstract
Migration of large-angle grain boundaries in ice bicrystals has been investigated by the method of capillary force developed by Sun and Bauer (1970 a, b). Strong anisotropy of the migration rate was observed between two cases when the boundaries moved parallel and perpendicular to the direction of rotation axis ω. X-ray diffraction topographic observations of grain boundaries (〈1010>/34〉) during migration by the capillary force revealed that they had a strong tendency to be parallel to low-energy facets and that the boundaries that were not parallel to any low-energy facets moved faster than those that were parallel. From observations in three specific directions of the normals of these facets, it was concluded that the facets were the high-density planes of the coincidence site lattice composed of two adjacent crystals. The anisotropy of the migration rate was interpreted in terms of the difference in the density of steps among facets: the non-faceted boundary with many steps moves faster than the faceted boundary with fewer steps.