Theoretical investigation of formation and diffusion mechanisms for point defects in ytterbium and lutetium silicates. Issue 1 (27th August 2021)

• Record Type: Journal Article
• Authors: Fan, Yun; Lai, Mengling; Zhao, Juanli; Yao, Yun; Yang, Lan; Liu, Yuchen; Li, Yiran; Li, Qian; Liu, Bin
• Is Part Of: Journal of the American Ceramic Society. Volume 105:Issue 1(2022)
• Page Start: 653
• Page End: 667
• Publication Date: 2021-08-27
• Subjects: defects -- density functional theory -- environmental barrier coatings -- silicates; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.18069
• Languages: English
• ISSNs: 0002-7820

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 SiO5 and RE 2 Si2 O7 ( RE = Yb and Lu) is uncovered. Furthermore, the nonstoichiometry related defects and phase composition in RE 2 SiO5 and RE 2 Si2 O7 is also studied. For RE 2 SiO5, Si RE · + O i ″ or Si RE · + V RE ″ ′ is the predominate defect complex accompanied with the RE 2 Si2 O7 separation under SiO2 ‐rich condition, while R E Si ′ + V O · · or R E Si ′ + R E i · · · is favorable under RE 2 O3 ‐rich condition. In the case of RE 2 Si2 O7, Si RE · + V RE ″ ′ or Si RE · + O i ″ is the favorable defect complex under SiO2 ‐rich condition while R E Si ′ + V O · · or R E Si ′ + R E i · · · dominates the defects, accompanied with the formation of RE 2 SiO5, under RE 2 O3 ‐rich case. Finally, the high oxygen migration barriers are revealed for both RE 2 SiO5 and RE 2 Si2 O7, indicating the low oxygen permeability in these silicates. These results will not only guide the future performance optimization of RE 2 SiO5 and RE 2 Si2 O7 through tailoring their composition, but also suggest their potential application as oxidation protective coatings.