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

Abstract

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.