Direct observation of basal dislocation in sapphire by HRTEM

Sapphire was compressed at 1400degreesC to activate basal slip, and the core structure of introduced basal dislocations was directly observed by HRTEM from a direction parallel to the dislocation line. It was confirmed that the basal dislocation dissociates into two half partial dislocations by the self-climb mechanism as suggested in a previous report. The two partials separated with a certain distance along the [0001] direction, which is normal to the glide plane. On the other hand, it was found that glide dissociation is not developed in the basal dislocation. This result implies that after the glide motion of the basal dislocation had stopped, glide dissociation makes a change to climb dissociation in the core of the dislocation. (C) 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.