Atomic Structure Characterization of Stacking Faults on the {1(1)over-bar00} Plane in α-Alumina by Scanning Transmission Electron Microscopy

The structure of a b = < 1<(1)over bar>00> dislocation formed in the {1 (1) over bar 00}/< 11<(2)over bar>0> 2 degrees low-angle grain boundary of alumina was observed by scanning transmission electron microscopy (STEM). It was found that the < 1<(1)over bar>00> dislocation dissociates into 1/3< 1<(1)over bar>00> partial-dislocation triplets with two stacking faults on the {1 (1) over bar 00} plane. The atomic structure of the {1 (1) over bar 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..., which is consistent with a former report. ABF-STEM image simulation was performed using structure models with the {1 (1) over bar 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.