Theoretical investigation of formation and diffusion mechanisms for point defects in ytterbium and lutetium silicates

Abstract Understanding the mechanism of point defects and the oxygen vacancy diffusion in rare earth ( RE ) silicates is important to evaluate their performance as environmental barrier coatings. In this work, the defect formation energies are calculated and the similar predominant native point defect type, that is, O Frenkel defect, in RE 2 SiO 5 and RE 2 Si 2 O 7 ( RE = Yb and Lu) is uncovered. Furthermore, the nonstoichiometry related defects and phase composition in RE 2 SiO 5 and RE 2 Si 2 O 7 is also studied. For RE 2 SiO 5 , or is the predominate defect complex accompanied with the RE 2 Si 2 O 7 separation under SiO 2 ‐rich condition, while or is favorable under RE 2 O 3 ‐rich condition. In the case of RE 2 Si 2 O 7 , or is the favorable defect complex under SiO 2 ‐rich condition while or dominates the defects, accompanied with the formation of RE 2 SiO 5 , under RE 2 O 3 ‐rich case. Finally, the high oxygen migration barriers are revealed for both RE 2 SiO 5 and RE 2 Si 2 O 7 , indicating the low oxygen permeability in these silicates. These results will not only guide the future performance optimization of RE 2 SiO 5 and RE 2 Si 2 O 7 through tailoring their composition, but also suggest their potential application as oxidation protective coatings.

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