| Abstract
| - We use first-principles density functional theory to investigate adsorption of Al, O, Hf, Y, Pt, and S-atomson the α-Al2O3(0001) surface. We identify stable adsorption sites and predict binding energies and structures.We find that Al, Hf, and Y preferentially adsorb on threefold-hollow sites, transfer electrons to the surface,and form ionic bonds to the three oxygen atoms. In contrast, the most stable adsorption site for Pt and S isontop an oxygen atom, and we do not observe significant charge transfer. We find a binding order of S < Pt< O < Al ≪ Y < Hf, which reflects both the ease with which the early transition metals Hf and Y ionize,as well as the (nearly) closed-shell repulsions influencing the adsorption of O, Pt, and S. We use these resultsto rationalize some observations regarding the stability of thermal barrier coatings.
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