A study was made of structural defects on the surface and cross-sections of single crystals that had been subjected to high-temperature (up to 950C) Zn diffusion. The defects were characterized by using X-ray techniques, optical microscopy, scanning electron microscopy and atomic force microscopy. The diffusion was found to lead to a deterioration of the structure; especially near to the surface. This process was associated with the movement of dislocations. Pile-ups of dislocations eventually generated cracks that were parallel to the {110} planes. The reaction between dislocations, moving on {111} planes that were inclined with respect to the surface, gave rise to perpendicular {110} cleavage planes which intersected the {111} surface plane along <211> directions. However, when one of the slip planes was parallel to the surface, the resultant (110) cleavage plane was inclined to the surface. Such planes intersected the surface in a <110>-type direction. The resolved shear stress that was due to Zn diffusion was proportional to cos[A]cos[B], where A was the angle between the stress axis and the slip direction, and B was the angle between the stress axis and the normal to the slip plane. It was clear that cos[A] for the {111} plane parallel to the surface was smaller. Therefore, the resolved shear stress was much smaller in this plane, leading to weaker cleavage traces in the <110> directions.

M.Azoulay, E.Grossman, H.Schacham, M.Mizrachi, A.Raizman: Journal of Materials Science, 1995, 30[18], 4527-34