Dislocations in Ice

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Abstract
The dislocation structures of dendritic ice crystals have been directly observed by x-ray diffraction topography. Growth occurs without the intervention of dislocations and very low dislocation dencities may initially prevail. Straining expands dislocations having 〈11[unknown]20〉 direction Burgers vectors from sources at grown-in inclusions. Slip of these dislocations in the basal plane (0001) and on pyramidal planes, probably (1¯101), with frequent occurrence of primatic punching, is observed. Dislocation reactions of the type (a0/ 3) [11¯20] + (a0/ 3) [1¯210] = (a0/ 3) [2¯110] and a strong preference for pure screw orientation are characteristic. These dislocations generally account for the known anisotropy of plastic flow in ice.