Structure of screw dislocations in a (0001)/[0001] low-angle twist grain boundary of alumina (α-Al2O3)

An alumina (α-Al2O3) bicrystal with a (0 0 0 1)/[0 0 0 1] low-angle twist grain boundary was fabricated by bonding two (0 0 0 1) substrates at 1500 °C in air. Dislocation structures in the resultant grain boundary were extensively observed in plan view and cross-sectional direction by transmission electron microscopy (TEM). The grain boundary consisted of a hexagonal dislocation network of 1/3〈12¯10〉 basal screw dislocations and wavy belt structures. The atomic core structure of the screw dislocations was analyzed in end-on view by high-resolution TEM. It was evident that the 1/3〈12¯10〉 basal screw dislocation does not dissociate into partial dislocations, which is in contrast to the 1/3〈12¯10〉 basal edge dislocation that dissociates into 1/3〈11¯00〉 and 1/3〈01¯10〉 partial dislocations. Also, TEM observation revealed that the wavy belt structures correspond to planar voids. From the morphology of the planar voids, it is considered that they accommodate a slight tilt component of the boundary.