Abstract:

The formation energy and diffusion barrier of oxygen vacancies (VO) were calculated using the first-principles density functional theory method, for the case of Ca segregated in the ∑3(1010) grain boundary of $\alpha alpha-Al₂O₃. The formation energy of Vo fell in the 3.05~4.04 eV range in the Ca doped grain boundary. This was roughly 2.5 eV lower than the undoped grain boundary. The activation energy of VO in the Ca-doped grain boundary changed to 2.30 eV, 1.8 eV less than the undoped grain boundary's maximum. Moreover, with the increase in the concentration of Ca, the crystal lattice near the grain boundary underwent significant expansion, further breaking the balance of charge. Therefore, the formation energy of VO was further reduced to -1.43 eV, and the diffusion activation energy was reduced to 1.27 eV. Thus, Ca doping proved advantageous in the formation and diffusion of VO in the grain boundary of $\alpha alpha-Al₂O₃.

Key words: alumina oxide, grain boundary, doping, first-principles