Diffusion mechanisms of vacancy and doped Si in Al3Ti from first-principles calculations

First-principles calculations were employed to study the migration of vacancy in clean and Si-doped Al3Ti. The effect of Si doping on the formation of vacancy and the diffusion of doped-Si atom in the Al3Ti were also investigated. It is found that, under Al-rich condition, the formation energies of Al vacancies in Al3Ti with Si doping are decreased compared with those in clean Al3Ti. The preferred migration paths of vacancies are not changed when Si occupies Al site, but the migration energy barriers for the majority of paths are decreased after Si doping. The doped-Si atom on Al site prefers to diffuse via the nearest Al vacancy.

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► In clean Al3Ti, both Al1 vacancy and Ti vacancy prefer the first nearest neighbor hop.
► In clean Al3Ti, Al2 vacancy prefers to diffuse via the second nearest neighbor hop.
► A proposed two-defect complex mechanism can decrease migration barrier of Ti vacancy.
► Both Si atoms on Al1 site or Al2 site prefer to diffuse via the nearest neighbor Al1 vacancy.