The characteristic triangular cross-grid dislocation structure in sapphire single crystals grown in the [00•1] direction by using the temperature gradient technique was investigated by means of X-ray diffraction topography. The dislocations lay on (00•1) basal planes and appeared primarily as three parallel groups of straight dislocation lines. At high temperatures, these dislocation lines could move easily on the slip planes and form different dislocation configurations via pinning, climbing and interaction. An analysis of the Burgers vector and image width of dislocation lines confirmed that three parallel groups of straight dislocation lines were of pure edge type, having <11•0>-type Burgers vectors, and a few dislocation reactions were of the type,

[11•0] + [1¯2•0] + [¯21•0]  0

A simple model of basal slip of the type, (00•1)<11•0>, was used to explain these dislocations.

X-Ray Topographic Observation of Dislocation Structure in Sapphire Single Crystal Grown by Temperature Gradient Technique. Q.Zhang, P.Deng, F.Gan: Journal of Crystal Growth, 1991, 108[1-2], 377–84