Molecular dynamics simulations of basal and pyramidal system edge dislocations in sapphire

To develop better understanding of the core structure of these dislocations and their potential role in the creep resistance of the alumina component in eutectics with tight [0 0 0 1] textures, a molecular dynamics (MD) simulation was carried out of the comparative core structures of both the (1/3)21¯1¯0 basal edge dislocations and the (1/3)1¯101 pyramidal edge dislocations on the (11¯02) plane in sapphire. The MD simulation revealed that the equilibrium structure of the core of the pyramidal edge dislocations undergo a dissociation into two half strength partial edge dislocations displaced vertically out of the best glide plane of cation holes with weak covalent bonding and possible fair glide resistance into two adjacent pyramidal planes of very strong covalent bonding, and consequent, very high glide resistance. While this explains the immobility in glide of such dislocations on the pyramidal system, no important structural impediment was found for their climb motion out of the pyramidal planes.