Dislocations and twinning activated by the abrasion of Al2O3

Defects generated at the surface of single crystal Al{sub 2}O{sub 3} during abrasion on diamond have been analyzed by high spatial resolution cross-sectional electron microscopy. Plastic deformation predominantly occurs by basal twinning and pyramidal slip 1/3(11{bar 2}0){l_brace}{bar 1}101{r_brace}. Basal twins have platelet morphologies, with widths d{sub 0001} = 2n{sm_bullet}1/6[0001] and {vert_bar}d{sub 0001}{vert_bar}{much_lt}100 nm, aspect ratios d{sub 1010}/d{sub 0001} or d{sub 1120}/d{sub 0001} > 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 {+-}{l_brace}11{bar 2}0{r_brace} and {+-}{l_brace}10{bar 1}0{r_brace} prismatic plane abrasion results in a more uniform 1--5% deformation twin cover with basal twin penetration {much_gt} that for basal abrasion. Extensive microcracking along {l_brace}1{bar 1}02{r_brace} 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 Al{sub 2}O{sub 3} are discussed.

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