Dislocation Behavior in Sapphire Single Crystals.
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MASS
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The investigation of large melt-grown sapphire crystals by X-ray transmission topography revealed an arrangement of basal dislocations generally described as tangles. Since present theories could not fully account for the tangle formation in sapphire, a mechanism involving dislocation reactions is suggested as a feasible explanation. Helices were generated by annealing thin sapphire plates close to the melting temperature. The axes of the helices were found to be parallel to the Burgers vectors, i.e., parallel to the 2-1-10 directions with no preference for a particular direction. Each helix observed was of an approximately regular shape, or possessed relatively constant pitch and diameter. The average diameter of the helices was about 50 micrometer. Mechanisms for the formation of cusp dislocations are discussed. Author