Atomic structure characterization of stacking faults on the ${ 11¯00 }$ plane in α-alumina by scanning transmission electron microscopy

The structure of a $b=<11¯00>$ dislocation formed in the ${ 11¯00 }/<112¯0>$ 2° low-angle grain boundary of alumina was observed by scanning transmission electron microscopy (STEM). It was found that the $<11¯00>$ dislocation dissociate-s into $1/3<11¯00>$ partial-dislocation triplets with two stacking faults on the ${ 11¯00 }$ plane. The atomic structure of the ${ 11¯00 }$ stacking faults was characterized by annular bright field STEM (ABF-STEM). The two stacking faults were found to have a stacking sequence of …ABCCABC… and …ABCBCAB…, wh-ich is consistent with a former report. ABF-STEM image simulation was performed using structure models with the ${ 11¯00 }$ stacking faults optimized by first-principles calculations. The overall features of the experimental and the simulated results agree with each other. However, slight differences in contrast were recognized in the vicinity of the stacking faults, suggesting that there are small differences between the observed structures and the theoretical models.