X-ray Diffraction Topographic Studies of Dislocations in Natural Large Ice Single Crystals

The method of X-ray diffraction topography was adopted to reveal the dislocation structure in natural, large ice single crystals which has been hitherto used for the extensive experiments of plastic deformation. The topographs show clear images of curved and straight dislocation lines lying on the basal planes of the crystal. Dislocation density is in the order of 10 4 cm -2 and Burgers vectors are ( a /3)<112̄0> or c [0001]. In many cases, edge dislocations compose the small angle tilt boundaries of which tilt angle is less than 1° of arc. Size of the subgrains bordered with such boundaries is in the order of 1 mm or more and it differs very much from the size of mosaic blocks evaluated from primary and secondary extinctions of X-rays. Another characteristic feature is that screw dislocations of one Burgers vector are much less than those of other two equivalent Burgers vectors of ( a /3)<112̄0> system.