Dislocation motion in ice: A study by synchrotron X-ray topography

Abstract

The synchrotron radiation source at the Daresbury Laboratory, Science and Engineering Research Council, has been used to obtain white X-radiation topographs of high-quality single crystals of ice with exposure times of about 20 s. Sequences of topographs show the motion of individual dislocations under stress in the very early stages of plastic deformation at temperatures from −10 to −35°C. Glide on the basal plane appears to be limited by a Peierls barrier in the screw and 60° orientations. Edge, but not screw, dislocations on non-basal planes glide faster than dislocations on the basal plane and act as sources of dislocation multiplication. The velocities of both basal and non-basal dislocations are found to be linear functions of stress. Much recovery occurs on the time scale of previous experiments to measure dislocation velocities. The implications of the observations for theories of dislocation mobility are discussed.