Dislocations and twinning activated by the abrasion of Al2O3 Original Research Article

Defects generated at the surface of single crystal Al2O3 during abrasion on diamond have been analysed by high spatial resolution cross-sectional electron microscopy. Plastic deformation predominantly occurs by basal twinning and pyramidal slip 1/3〈1120〉{1101}. Basal twins have platelet morphologies, with widths d0001=2n∗1/6[0001] and ∣d0001∣≪100 nm, aspect ratios d1010/d0001 or d1120/d0001>10, and ABCBA stacking of (0006)Al planes across twin interfaces. Basal twins and dislocations occur clustered around steps in macroscopic (0001) abraded surfaces, whereas ±{1120} and ±{1010} prismatic plane abrasion results in a more uniform 1–5% deformation twin cover with basal twin penetration≫that for basal abrasion. Extensive microcracking along {1102} rhombohedral and (0001) twin habit planes occurs, but no widespread rhombohedral twinning, prism glide or non-basal dislocation Burgers vectors were observed. Implications for surface preparation of Al2O3 are discussed.