Cr diffusion in α -Al₂ O₃: Secondary ion mass spectroscopy and first-principles study

Diffusion in α -Al₂ O₃ has been extensively investigated for several decades but its atomic-scale mechanism is still in controversy. In the present study, cation diffusion in α -Al₂ O₃ was investigated by secondary ion mass spectroscopy (SIMS) and first-principles calculations. The SIMS experiment revealed that Cr diffusion in α -Al₂ O₃ shows a crystallographic orientation dependence. Specifically, Cr diffusion perpendicular to the [0001] direction is more preferable than that parallel to the [0001] direction. It was found by theoretical calculations that both Al and Cr diffusion mainly proceeds via a vacancy rather than an interstitial site. In addition, theoretical calculations predicted that the crystallographic orientation dependence of Cr diffusion is stronger than that of Al diffusion. By examining the atomic structures around the migrating atoms, it was found that the migration energetics are closely related to the interatomic spacing along the migration path.