Studies of Crystal Imperfections in Ice with Reference to the Growth Process by the use of X-Ray Diffraction Topography and Divergent Laue Method

This paper presents studies on crystal imperfections including basal and non-basal dislocations, small-angle grain boundaries, stacking faults, and dislocation networks in ice using both X-ray diffraction and Laue techniques; these studies examined the growth process or origin of the ice, i.e. ice from glaciers, ice grown from the melt, or ice formed by sublimation. Several hoar crystals were found to be perfect, dislocation-free crystals, this may be due to their very slow growth rate. Dislocations and Shockley-type stacking faults were observed in some crystals. Dislocation density of a hoar crystal is very large at the point at which it started to grow, but away from this region the density becomes so small that no dislocation can be seen. The arrangement and structure of dislocations around vapour figures were also studied by means of X-ray diffraction topography. It was found that the dislocation density is high along the periphery of the vapour hexagon and that the great majority of dislocations within the hexagon are running from its centre towards the vertices or sides of the hexagon. Long screw dislocations with Burgers vector c <0001> were observed in a tabular ice which was formed artificially at a very slight degree of supercooling. The behaviour of dislocations in ice subjected to a tensile stress was studied by the use of the divergent X-ray technique which gives both enlarged Laue spots and a transmission pattern in the same photograph.