The velocity of dislocations in ice

The velocities of dislocations in single crystals of ‘pure’ ice between −4 and −39°C have been measured by white radiation topography using synchrotron X-radiation. Dislocations glide on basal planes as straight segments in screw and 60° orientations with velocities directly proportional to stress. The screw segments have a velocity at − 20°C of 0.8 μm s⁻¹ MPa⁻¹ and an activation energy of 0.95 ± 0.05 eV. For the 60. segments the velocity at − 20°C is 1.6 μm s⁻¹ MPa⁻¹ and the activation energy is 0.87 ± 0.04 eV. Edge dislocations on non-basal planes have higher velocities of 18 μm s⁻¹ MPa⁻¹ at − 20°C and a lower activation energy of 0.63 ± 0.04 eV. These dislocation mobilities are discussed in terms of the theory of kink propagation across a Peierls barrier and the effect of proton disorder in the ice.