X-Ray Topographic Studies of Dislocations in Vapor-Grown Ice Crystals

Abstract

Abstract Ice crystals grown from the vapor under controlled conditions have been examined by X-ray topography. Plates grown in the region — 1.5°C to —3°C and at — 15°C near water saturation were often free of defects, as were plates grown at smaller supersaturations (1.5% at — 3°C, 6% at — 15°C). It is inferred from these observations that growth was occurring by two-dimensional nucleation on the prism plane. It is suggested that multilayer adsorption on the crystal surface was responsible for growth at the low values of supersaturation, compared with higher values predicted by the Burton—Cabrera—Frank theory. Ice crystals dependent on dislocations for growth could only occur at supersaturations lower than these values. The crystal habit is interpreted as being dependent on differential two-dimensional nucleation on prism or basal faces. Rib structure is often associated with dislocation loops; stacking faults were evident in some crystals.