Pyramidal edge dislocation cores in sapphire

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In sapphire single crystals of [0001] orientation and in directionally solidified eutectic ceramic composites having topologically continuous Al2O3 components of nearly perfect [0001] growth textures, creep resistance in the 1400–1800°C temperature range results from the sessile nature of the dislocations of the pyramidal system which is the only system, to produce creep in this orientation. Here we present results of a molecular dynamics simulation of the core of the pyramidal edge dislocation that demonstrates its sessile character and indicates that the only viable option for creep in this orientation is by the climb of such dislocations.