Nanoscale ductility in c ‐plane Al ₂ O ₃ : Dislocation and twinning mechanisms via nanoindentation and molecular dynamics

Brittle oxides, such as α‐Al 2 O 3 , i.e., sapphire, are traditionally unsuitable for ductile applications, yet exhibit enhanced plasticity at nanoscale. This study explores the mechanical behavior of c ‐plane‐oriented, dislocation‐free monocrystalline α‐Al 2 O 3 via molecular dynamics (MD) simulations and experiments, including nanoindentation and post‐indentation TEM analysis. The results demonstrate high strength with homogeneous, extensive deformation without failure. Plasticity is dominated by basal (0001) dislocations and rhombohedral [102] twins, which nucleate at deformation onset, as confirmed by MD and TEM. Generalized stacking fault energy (GSFE) and twinning fault energy (TFE) calculations elucidate mechanisms that mitigate crack initiation and propagation on the c ‐plane, aligning simulations with observations. These insights advance the understanding of nanoscale ductility in oxides, broadening the utility of sapphire in load‐bearing micro/nano devices.