The motion of non-basal dislocations in ice crystals

Abstract

The dislocation structure in ice crystals has been extensively studied using etching techniques. There is a general consensus regarding the motion and structure of basal dislocations. The opposite is true concerning the motion of non-basal dislocations. This paper presents experimental evidence of the motion of non-basal dislocations in ice, as revealed by etching and replicating. Two distinct etch patterns caused by the motion of dislocations emerged on the basal plane were observed. One is a series of separated flat-bottomed etch pits, corresponding to the jumping motion of the edge dislocations. The other is the uniform zigzag etch channels, corresponding to the cross-slip of the screw dislocation on the prismatic or pyramidal planes. Special attention is paid to the cross-slip of 〈11 23〉 screw dislocations which can contribute to the plastic deformation along the c axis. An important consequence of the intersection mechanism proposed in this paper is that, while the basal deformation of single crystals of ice may be described in terms of slip of the basal dislocations, the non-basal deformation of ice crystals and the plasticity of polycrystalline ice are controlled by the motion of jogged non-basal dislocations. Given that the intersection of basal and non-basal dislocations contributes to the anisotropy of plasticity of ice crystals, the latter assertion implies that the rate of plastic deformation of polycrystalline ice should be climb dependent.