Pyramidal edge dislocation cores in sapphire

Abstract

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.

Acknowledgements

This work was supported by the US Air Force Office of Scientific Research under grant F49620-99-1-0276, and by a NATO Science Fellowship (to C. T. B.) from the Türkiye Bilimsel ve Teknik Arastirma Kurumu. We acknowledge useful discussions with Professor B. Wuensch of Massachusetts Institute of Technology and Professor A. H. Heuer of Case Western Reserve University on the relaxed real coordinates of ions in sapphire and suggestions of Mr J. Yi for useful clarifications in the text. For the computations we used the resources of Professor S. Yip of Massachusetts Institute of Technology.