Quantitative HRTEM Investigations of a Symmetrical Tilt Σ11 Grain Boundary with Two Different Grain Boundary Planes in -Al2O3

Abstract

High resolution transmission electron microscopy was used for the determination of the Σ11 grain boundary structure in α-Al2O3. Two orientations of the Σ11 boundary were investigated, the (101¯1) and the (2¯116) interface planes, respectively. The atomistic structures of the grain boundary core were quantitatively determined by comparing the experimental micrographs with simulated images. Each GB was imaged along two perpendicular directions. 3D models are proposed for each of the grain boundary orientations. For the Σ11 (101¯1) grain boundary an empirical shell model was used as the starting model for the structure refinement, whereas a CSL type model was used for the Σ11 (2¯116) grain boundary. After the quantitative evaluation both Σ11 grain boundaries revealed that the best matching structures were non CSL model structures. Non-mirror symmetry was observed for both configurations for at least one investigated zone axes. For the Σ11 (101¯1) interface a relative shift of one crystal halve with respect to the other was observed perpendicular to the grain boundary plane, where the (101¯1) lattice spacing is reduced by Δy = 0.04 ± 0.01 nm. For the Σ11 (2¯116) interface the resulting atomic structure is shifted by Δx = 0.322 ± 0.035 nm in the [21¯1¯1] direction from the CSL model structure. This corresponds to half of the repeat length of the [21¯1¯1] direction. No relaxation perpendicular to the interface plane was detected.